how hot is it in your area? Does she have gut noise? Is she rolling ? What is her gum color? Nostrils flared ? capillary refill time, by pressing on her gums and counting how long it takes be pink again, . Any weeds in the hay or pasture? free choice salt? Is she drinking? eating ? Pooping? peeing ? How long has she been laying down ? Abnormal behaviour for her ? Is she sweating all over or just in her chest and flank areas ? If you grain her, check for moldy grain, any oppossum or raccoons in the area? Has she been vaccinated ?
There are a lot of things to consider. If you feel she is Off, and are concerned, you can watch and wait, or call out the Vet .