Do u know why a bath makes baby move?

Im only 17 weeks pregnant and for the last two days when I get into the warm bath at night I can feel my fetus moving. At first I thought I was crazy, but she doesn’t stop moving. Is this normal? Why does she only move when I’m in the warm bath? Doctor said I can take warm baths and they help me so much, but I really want to know if anyone knows why by 17 week old fetus has a party (or a meltdown) every time I get into water. Anyways I am thankful for any answers or advice. Also water isn’t hot it’s just warm enough to get the chill of winter off my mind. Thanks 🙏🏽 and please be kind with responses!