Baby slamming legs down while sleeping at night

Does anyone else’s baby do this? My son is 15 weeks and it’s just recently gotten worse. He will start doing it out of the blue at some odd hour of the morning . We will get up to check on him and his eyes are closed and he’s sleeping . He’s also started wiggling his way to sleep sideways in his pack n play . I lay him in the center when we go to bed and by the time morning comes , he’s sideways lol .