F19 my younger brother got hard with my head in his lap

Me and my brother we both live together in an apartment I rent , it’s pretty chill and we like to smoke weed together. Me and him we had just smoked and we were watching a movie together and I was just resting my head in his lap. I was wearing just a little black singlet and some shorts and after a few minutes I felt something against my head , I didn’t want to make it obvious but when I sat up I looked down and saw he was so hard . I didn’t want to make him embarrassed or anything so after I got us both a drink something alcoholic and I kept on cuddling with him watching the movie.

I don’t know the situation is all a little weird I’m not sure if I should talk to him about it, I’m not sure if it’s normal he got hard near me like that.