I wouldn't worry at all. The doctors won't worry until you're about 28 weeks. I know it's super stressful because it's the only way we can tell that they're okay... But babies can sleep up to like 16 hours at a time in the womb... and with you being 24 weeks, your baby is still very small and they may just be turned towards your back so you can't feel them kick.
Just lay on your left side drink some orange juice or ice cold water and he'll get movin!! I went to LD when my son was acting up and he was okay. Just being lazy and was running of room. But yeah just drink something cold see if he wakes up
My son is like that. He will be so active and busy for like 3-4 days straight then he sleeps for 3 days straight lol. Even though I know it's his schedule and how he is, it still freaks me out every time