If you've already had two chicks die, that's a clue you may need to intervene.
Please, answer this question, is your brooder large enough where it's around 85-90F or 30C just directly beneath your heat source, and I'm assuming you're using a heat lamp, and around fifteen degrees cooler everywhere else in the brooder?
If it's equally hot everywhere in the brooder, that could be your problem. Use a lower wattage bulb or raise the heat lamp up higher.
What does the poop look like? Especially, did you notice any red in it? You may have coccidiosis and need to treat with amprolium, even if feeding medicated feed.
Have you checked for pasty butt? It stems from overheated brooders, but sometimes chicks are just prone to it. If you don't keep little vents from crusting over, chicks will die from not being able to pass waste.
Normal chick behavior in the first several days is to be active and curious, interspersed with sudden comatose behavior where they simply collapse anywhere they happen to be at the time sleep overcomes them, but then they are up and off to the races once again, then it's collapse time again.
At night, if you happen to be able to block off the light, they will sleep all night long.
I recommend you ditch the heat lamp all together, and use a heating pad. there are no over heating and fire dangers with this system, and the chicks get natural night time and will be more relaxed and healthy for it. Read about how to set it up on the thread "Mama Heating pad for the Brooder".
If you have a coop, you can also be brooding in it, avoiding the confines of an indoor brooder box and over crowding. You can read about that in my article linked below under "Articles by azygous."
