6 month old tries to fall asleep but keeps waking himself up.

My 6 month old sleeps fairly well except when he moves. I know that sounds stupid, but that’s the best way I can describe it. He’ll lay on his back and push his knees up and his fists in his eyes in a ball and fall asleep for 10 seconds. But then his body relaxes and it jolts him awake. Anyone experience this? We’re trying the Ferber method right now because it worked for our daughter, but it’s not going too well with him because he wakes himself up.