Horse Anxiety

Hi everyone, I have a problem, I don't know why but my horse is pacing back and forth infront of the gates in her pasture at a walk and trot and sometimes a canter. I can't lounge her becuase no one is home and everyone is busy but I think she's anxious about something? I usually like to run along side her pasture and she will race me but today she won't. She just paces and when I leave her and go in the barn for a minute she gets faster and her eyes get real big. Any ideas on whats bothering her?

Has anything about her surroundings changed? Did a buddy of hers leave?
Could she be in heat? Could she be sick?

No she hasn't had any changes. I looked her over and theres nothing physical.

Is it really hot? What about flies? When I was living in MA at a stud farm, the broodmares would get so antzy mid day because of the heat/humidity, and the horse flies. We'd bring them in a little after noon so they'd be more comfortable.

I figured she was too hot but when I took her in her stall she paced even more and when I left I heard a whinny and I looked behind me and she was rearing!

Wonder if someone rode by on another horse and she's just wishing she had company. Esp if she's in heat, sometimes the mares are crazier than the stallions to find a mate. I'd leave her out if she's worse in a stall. Locking her up may make her more frantic. At least outside she's able to see and can burn off the energy. (unless of course shes' attempting to push on the fence or jump it, then the stall might be a better idea)

Yes it would make more sense if there was another horse. She's the only horse for like miles and she was just in heat, she's out of it now. Gosh she's still pacing out there!