AIO? My 23M boyfriend held me 19F underwater during a bath to prove a point and I’m still shaken

I’m 19F and have been with my boyfriend 23M for over a year now. We come from different countries and religions but we’ve made it work. I have to mention this. My boyfriend loves turning everything into a competition. We both go to the gym and he's always like "who can do this better" Even at home he’s always asking who can cook better.. clean faster.. you name it.

A week ago we were relaxing in the bathtub together. He asked who I thought could hold the other underwater the longest. I found it weird and just brushed it off as one of his usual questions. Just 2-3 minutes later he got up as if to get out of the bathtub and suddenly pushed me underwater. He kept me under for what felt like more than 20 seconds. When he finally let go he started laughing.

I’m generally healthy but I have a heart condition that requires daily medication to keep my heart rate normal. Without meds, my heart rate can go up to 140-150 bpm. Even with meds, sudden situations like this can make my heart rate spike to 140 and stay between 110-120 for the next few days. He knows this.

He brought up what happened today and said he apologized (which he didn’t) and that I should get over it. I'm trying. He said he was trying to prove a point. That I need to work on myself more. It doesn't make sense to me because he’s naturally stronger than me and no matter how much I work out. I can’t always defend myself against everything successfully.

I can’t talk to my sister or mother about it. They’d just ask what I was doing in a bathtub with a guy in the first place. And I still don't have friends here. It's only him and me. We’ve talked about it more than once and he says if I did this to him he would've found it funny. I don't know if I just need to loosen up more but I don't understand how holding me underwater for that long was ever funny in his head.

Edit: He’s also complaining now about the marks I left on his wrist/arm (almost faded). I didn't mean to. It was sudden and I swallowed bit of water and I was freaking out and just wanted him to let go. I apologized for this but told him it was a natural reaction to what he did.