Something wrong or just a chill chick?

Hi all! first time having chickens, we lost two earlier this week so I'm a bit stressed making sure they are all happy, I have one Plymouth Rock that just seems to act a bit different than the others. She's eating/drinking/pooping just fine but will often times go lay down directly under the heat lamp while the other ones run around. I have them on the same medicated feed they were on at the farm store and have chick boost in their water so I don't think it's anything nutritional but I don't want to lose another one. If I'm being dramatic please let me know!