Alarming GP behaviour

Question
My Guinea Pig is almost 4 years old and has been in excellent health recently. (his 6 monthly check up was about 8 weeks ago)Two nights ago he began running around the cage, now he does this when he is happy and playful but this was different. He ran so fast he kept banging off the sides of his cage then jumping up vertically as if terrified and wanting out. It was quite violent and lasted about 3-5 minutes. Last night there was a similar shorter incident, inbetween times he has been sitting in the on place and backing away from me and sometimes backing away from nothing. He is very jittery and jumpy.He will let me pick him up and makes the normal noises of comtentment when on my knee and is definately more settled than in his cage. He isn't really going to his dish or water bottle as the corner he has chosen to sit in is at the other side of his cage. Yet when I hand feed him with vegetables he devours them and I held the bottle for him and he drank a bit. This is highly unusual behaviour as he is usually extremely passive and friendly. I took him to the vets this morning, no mites,coat is good,teeth are fine, he is going to the toilet but maybe less than usual, she feels his eyesight isn't great although she thinks he has some and queried the possibility of diabetes. She gave me pain killing medicine for four days to rule out pain but I dont think it is pain, it seems like fear. I'm sorry for the length of this letter but I have tried every website and book I can think of. I am at my wits end. Any advice at all would be appreciated.

Emma

Answer
Emma --

Well, it may be that your guinea pig is needing a bit of exercise.  This type of behavior (called "popping") is usually observed in guinea pigs who are cooped up or restless.  Try letting him out of the cage to wander (in a safe, controlled environment, of course) a bit.  Popping is the jumping behavior you noticed -- guinea pigs can jump up to two feet straight up, usually when you startle them, but also sometimes when they have a bit of excess energy.  It could also be the food you are feeding him.  Have you changed his diet in any way recently?  A different brand of food, different veggies, etc?  If so, that could be the problem -- try switching back and see if the behavior settles back down.  

If none of this seems to help, I'm going to create you some homework.  I want you to observe when he seems to be the "craziest" and write down anything that happened right when he started.  We'll see if we can find a trigger.

Hope this is helpful.  Good luck, and don't forget to keep me updated!

Lorena