Swinging hands, turning head till awake

Hi all, my kids just turned 5 months and is unable to sleep well at night recently due to her swinging of arms, legs, flipping her head left & right frantically & whining while in her sleep. On a few occasions, she does that till she wakes up and cry. She seems to fall back asleep if I gently hold her hands down for a couple of mins. Anyone know what’s she trying to do?