@coded_artist @Silverwolf @ClearSky @brimshae @BasedLordEndless thanks to everyone for your kind words and prayers, I'm convinced that helped.
After being almost inactive for a moment he started to slowly stretch with a lot of force, disforming the belly, which only reminded me of people's bodies having a muscle reaction and going straight after going without oxygen due to a choke or hanging, it was terrifying.
But then he slowly started to act like usual, and then seemed to happily move and kick as usual all night, which reassured us, he seems to be perfectly fine now. We have the first appointment of the day at the obstetric clinic to talk to those useless people and see him on screen, but according to endless research on Internet he most likely did got entangled in his cord and fought against it. He's a strong boy.
Thanks everyone.