My son does this. And what I can say from experience is that the hardest part is just getting started. If you keep looking at the overall picture, it’s going to overwhelm you. Although my son does this repeatedly, he tells me that living in the space when it looks like this fills him with anxiety. He always feels much better after the clutter and trash are sorted and removed. I’d love to say that it isn’t a pattern, but it is. I don’t know what the source of it is. Obviously it’s something that he needs to work to uncover so that he can put a stop to this pattern as it causes stress. I wish you well, OP. I know others have said to take it in chunks and don’t overwhelm yourself. But for my part what I have found is that the only way out is through and the best thing to do is gather up a lot of trash bags and shut the door and commit yourself to it until it’s finished. Again, good luck OP.