For example, the AOE (area of effect) spell "Cloudkill":
When a creature enters the spell’s area for the first time on a turn or starts its turn there, that creature must make a Constitution saving throw. The creature takes 5d8 poison damage on a failed save, or half as much damage on a successful one. Creatures are affected even if they hold their breath or don’t need to breathe.
Say you cast this in a 15x15 room. It should cover the entire room, and as such, the question remains - are you affected by the cloud, as well as the enemies?
I'd hazard a guess as yes, as it doesn't specify "other than you," but I just want to make sure so I don't cast it and TPK by accident.