My (22F) sister’s (27F) husband (28M) came into my bedroom last night and something strange happened.

I’m still very confused right now so sorry if this post is all jumbled up.
I’ve been staying at my sisters house lately. She lives four hours away and I’ve been staying with with her these last few nights. She lives with her husband of 4 years. I have a very good relationship with her but her husband and I are not close at all. He’s always very standoffish and we never talk to each other. I’ve probably exchanged 5 words with him in the last 4 years. We tend to stay out of each other’s way. This is especially bad considering the fact we see each other a lot, we’re a tight knit family so my sister/parents and I are always around each other. At first I thought this was simply his character and so I didn’t take it personal. Then I realized that he’s actually quite warm and welcoming towards other people. He’s all smiles and jokes when it comes to others but he’s never been nice to me. It’s clear that he just doesn’t like me. I don’t know what I did to him to deserve this but I’ve accepted it and honestly don’t care. (He was good to me on one occasion though. One day I was swimming at the beach and scraped my arm against some sharp rocks. The wound wasn’t terribly painful but he used a first aid kit to treat it and I felt a lot better. But this still didn’t change our relationship). Anyway, my sister is well aware of the fact her husband and I are practically strangers to each other. Whenever I bring this up, mostly in a lighthearted way, she gets very irritated though.
Now I got that out of the way, l’ll explain the issue. Last night I fell asleep at around 2am. A short while later I was awoken by the feeling of somebody being on top of me. I opened my eyes and it was him. The room was dark but I could see him thanks to the moonlight. I was VERY sleepy and confused and asked him what he was doing. He was staring at me and looked very sad and teary eyed. He looked so sad that I thought someone had died and it freaked me out. He started touching my face and then put his hands on my throat. At this point I tried to get him off me but I couldn’t. He lightly slapped my face to make me stop and then started choking me slightly. It wasn’t a strong choke but definitely enough for me to feel some pressure. After a few seconds his grip tightened and he leaned over like he was about to kiss me(??). He didn’t though and instead looked at me with a sad expression for an uncomfortably long time. I literally told him “get the f*ck off me or I’m gonna screamâ€. He sighed and got off me. I locked my door and fell asleep soon. I was feeling more confused and shocked than scared. He seemed very emotional and I’m struggling to understand what that was about.
This morning my sister was out jogging and I found him in the kitchen. I asked him about last night and he claims that he doesn’t remember a thing because he was drunk. Maybe he was drunk but I know that he remembers what happened. I told him that he was lying and he got angry. When I brought up the fact he choked me he said that I shouldn’t make up stories like that and make my sister jealous because that’s her favorite (tmi). I told him to never touch me again and my sister came back just as I was leaving. A few minutes later I heard them arguing and I could tell it was about me. My sister hasn’t spoken to me since and I have the nagging feeling that she will tell me to leave.
I’m wondering now, what should I do? Should I go ahead and tell my sister? Should I tell my parents? I’ve never been in a situation like this and I have no idea how to handle it. It’s just all very weird to me. I hope my post is clear enough but I can answer some questions if you have any.
TL;DR I’m not close with my sister’s husband. We hardly ever talk to each other and he made it clear to me that he’s not interested in being nice to me. I accepted this and as a result stay out of his way. Right now I’m at my sister’s house and he came into my room last night. He got on top of me and choked my slightly. I’m confused and weirded out by his action and don’t believe his claim that he doesn’t remember doing it. This morning I told him to never touch me again otherwise there would be consequences. My sister came back, they proceeded to argue and now both of them are ignoring me. What should I do?


Source.

It's not what you should do, it's what you should've done when the BIL was actually in your room.

@Sparky: I would never say a thing to protect your sister. I will find a way to see what that was all about though.