Do you think horses can get dark circles under their eyes?

Sam is in training! One of the ladies at the paddock is an instructor and she is helping me with Sam. For the next two weeks I am not allowed to ride him - she is riding him and does not want me to undo what she is trying to teach him. I asked her to ride him for me about a week ago know and really liked how quiet in the saddle she was but still asked firmly until he did the right thing then let the pressure off. I try to be there for his training sessions but sometimes Jane can only get out there while I am at work. We will taper it down so I will have lessons while she is still riding him. She works on the same principles as me so that is awesome.

I arrived at the paddock this afternoon to feed Sam and even walking to his paddock I could tell something was different - he was exhausted! He looked like he had dark circles under his eyes! Poor little thing. Under his eyes the grey was really dark! I know Jane wouldn't do more than he can cope with. I led him out to get another rug for him and he followed quietly - didn't try to to grab grass on the way. When I threw his lead rope over the gate to get his feed he dropped his head and snoozed instead of seeking out food.

I spoke to Malcolm (the owner of the property) to see if he saw Sam being worked and he said that it didn't look like Sam was ridden that hard. I didn't see Jane to see how the session went. Sam was happy to eat his dinner so I will see him in the morning and see if he has recovered.