Is it normal to listen to my parents have sex every night?

I [used] to sleep in the lounge with my parents when it got too cold (My parents wanted me to sleep in the lounge) but went back to sleeping in my bedroom because I got tired of hearing my parents have sex. When I did sleep in the lounge, they would always start doing it as soon as they think I'm asleep, but no they're always wrong.. because i'm actually still awake and It actually takes hours for me to go to sleep because I suffer from Insomnia, I felt bad that I wanted to sleep back in my room so that was what I did. Now.. They seem to get really pissed off at me easily only because there are times when Im busting to go for a pee I would walk into the area of the house where the toilet is next to the lounge area, when I do go, I would here them quickly making these panick modes where they would pretend nothing was going on, this is not the first time but.. tonight I went to go use the toilet and heard them and they said something like they didn't like the fact that I disturbed them when I accidentally banged into the tables and chairs when walking out of my room because I couldn't see in the dark, they had all the lights off and sometimes they would turn the wifi off just so that they make sure im asleep! Is this normal?