It looks like somebody has to start

When I'm coming back from my university city to hometown and my dad's house I immediately fall into something like dark cloud of energy. I wanted even to clean this place with energy, but after few moments in that house I start to doubt that I can do things like that at all. After comeback to my own flat I fell sick and emotional unstable whole next day. Even SWEET and grounding don't help me much.
It's my home and I can't stay there - it's ridiculous.

Even when my mum still lived in that house there was something wrong with atmosphere. Year by year it was harder, but after I moved it's hard for me to come back there. Last owners of that place also had divorced so it looks strange.

When my mom first time came back to this place after he moved out he felt like something heavy wanted to smash her into ground and suck whole energy. She shoot out crying.

Someone has any feelings/thoughts about that?

It sounds like one of those instances when negative energy has seeped into the walls etc. - which is part of the reason why, when we ground, we need to make sure it is actually going somewhere where it can be recycled, not walls or chairs or anything like that.

If you're set on clearing the energy, you could start with something simple. Before I knew about energy the way I do now, sometimes I would draw a chalk circle on the carpet in my room. I'd sit in the circle and make the space within the chalk line completely mine. I used it more to shut out outside stuff - like if I'd had a fight with my mom and I just wanted the space to think. This may be exactly what you want though. Then you can expand the circle a bit each time.

The chalk lines vacuum up pretty well, or you can just rub them into the carpet when you're done.

I had that in my previous apartment. There was something there. I even had recurring dreams about a shape standing at the foot of my bed, dreams I didn't have when I was sleeping somewhere else.

Now my bigger problem is disability to start doing anything. If I'd like to clean this place with help of energies I'd had to go there when it's empty. My father believes that any energy work is work of devil so It's hard to do anything when he's around.

Somehow it may be test for me. Can I clean dark energies in right way and for long time. When I'll find possibility to start It'll go easier, but now I need power to avoid distraction.

If your father thinks it is part of devilish work then the following is totally ok with him. Why? Because you can tell him the truth. You are cleaning the room the way the old Christians used to do it.
So for this you first need to identify where the hot spots and heave spots are. This you can do by sitting in the middle of the room and extending your (3rd) auric field so that it expands the while room. Then just feel where the spots are..

Or you can sit or stand and shift to auric vision and simply see the places where the energy hangs. Just see where the dark (often brown of blackish mixed with dark reds and someimes fire yellow) are. Keep your emotions out of this scan, just notice and find the spots.

Or (yes there are many ways to do this) you can use your lower arms on the inside (or your palms) and slowly walk through the room and feel the tingly/hot/slow/sluggish/sticky/.. spots.

Ok so now I assume you can find the spots in whatever way. Get at least two bells, one with a lower heavier sound , one with a light sound. Dont!! use electronic ones. Get the real ones and clean them before properly.
You need to get two types of incense. I assume you have little or no knowledge about incense so in this case you should trust your smelling capibility. You need one heavier incense but not too heavy (rose incense is a fire/wood type which is often good) and one light one whic should smell good and not heavy at all. Be aware not to get too much indian incense on sticks, if at all possible get the incense that is made out of wax like drops.
So now the work you need to do. Walk around your room and use the heavy bell first cling it several times on several spots in the room. Specially near the hot spots. It'll make the energy loose its anchor. WIth it you need to walk aroung with the heavier incense. Walk until you see that the clots (specially in the corners) are dispersed. Now it is time to go back and get the lighter bell and the lighter incense. Do the same with these (it should take longer).
Open the windows, charge up your hands and forewarms and collect the shattered energy remains and simply toss them out of the window or better yet feed them to the plants or trees (they eat this and it is actually food for the plants).
Once that is done, leave your room, take a shower (not with hot water) and let the room rest for at least 30 minutes.
Then when you get back check if all the dark energy is gone, it should be but you may have missed spots. If so then repeat this procedure again...

Now about your father.. This what you just have done (except the first path, the feeling/seeing/registring the dark energy and where it is) is simple the old way of how rooms were energetically cleaned. It has been in use for centuries even by the christians in their churces (who do often not really know what they are doing...)
Once you are done get a few plants in your room and you are done.. Make you own ritual for your own room.
And every now and then do an energetic cleaning in your room, specially if there were heavy emotions in the room.

Now about how to explain it. What is described here is the way to clean a room of more coarse energies that are harmful. It has been used for centuries and is used in the churches as well. Although in the churches it is often unknown of how it is done, let alone that it is done properly.

And do you know from where this energy is coming from? I mean: is it sth there which "stuck" there, or this house gathering bad energy? I used to live in such house which was like a muddy pond - low energy was gathering there, and nothing was coming out. You could clean it and clean and clean, and after some time energy was again "muddy". We moved from this place now and as far as I know current owner "stuck" with that house too. They are planing destroy it and change completely that area, so I hope, energy of this place will change for good. And how is energy-flow in this house and surroundings?

Lastly I discovered something amazing about that dark energy in my house. It was caused partly by my relation with mum. How is that?

I couldn't accept that my mum don't care about me emotionally, because she was caring about me physically a lot. I was always telling myself that she is nice, she love me and she care about me. she don't because she can't and don't know how to do it. When she moved out form my home my dad started to tell me each time when I was visiting him: 'Look what she is doing to me, your brother and to you. She don't care about you!" etc. I didn't liked it and tried even harder to hide my own emotions inside my guts. Making more and more mess inside. That's why every time I was visiting that house I was loosing whole energy and felt dead. I was killing myself energetically from inside.

Lastly I accepted scary truth about my mum, agreed with dad, not completely but in my own way and talked few times with my mum about whole situation. Whole energy of my home has changed in one moment when I accepted that feeling inside me because that energy wasn't fact my inside energy. This weekend I'm visiting that house second time since then and I feel that visit will be a lot better

Dark energies (generally also heavy and coarse) come up from powerfull emotions. Ones like anger, hatred, disgust, treason, and such cause your own (and the other persons) energy levels to grow a lot more coarse. When you are in such a state then the higher energies no longer appear. The higher energies are generally finer usually one or more octaves higher. When you are caught in such an emotion then the ego starts to spin them around, your thoughts get stuck on that emotion. You recycle sentences in your head e.g. why did she ..., am i ...., etc.. Observe your thoughts carefully, or speak them out loud and record them on an mp3 player. You'll notice quickly that there are loops in it and you repeat the same thoughts over and over again. This is how you strengthen these energies. Next to that the thought are often projected and thought in a certain place. E.g. on sitting in a closed position with the chin down and the body somewhat caving in. This causes compression and it closes the front of the chakras of. Energy, specially the more coarse energy tends to gather in corners like dust. Where it clutters sticks and stays sometimes for years.
I clearly see a conflict in you that to be honest is not your own, you accepted it from the words of other people. if you trust your heart (as the saying goes.. actually you trust your instinct, your common sense and your heart) you can see that whatever is said does not have to be true. People talk in limitations, liek the statements you mentioned. Instead you can see what options there are, see where you yourself can nudge in some freedom for yourself and some love for your mother. Maybe she never learned how to show love due to circumstances. One thing you can do regularly that will melt her is when you feel warm in your heart to give her a well ment hug and feel it fully (can be quite emotional dont worry about that it is good that it happens).
It is great that you already took steps on your own...
One word of caution, people tend to think singular. This meaning that they think they know THE reason why such and so... Often it is only a part of what is going on. The deeper you look the more you will see. The beauty is that if you look very deep then you will see through the sticky stuff. Dont make it too personal tho, because if you do it the wrong way it'll become sticky and you'll start thinking sentences like 'I am ...', 'I want ...', 'I feel ..' etc.. on a very personal level, instead of simply noticing a dark energy.
Kudos for talking to your mum that was great work!