Witness it happened to my friend's daughter as well and she is only 11. He told her to get his car key and half an hour later she forgot that she already did that. We think this is just a one time coincidence thing, but turns out it happens quite frequently.

Cut the long story short, he found out that his daughter has poor blood circulation. So the brain doesn't get enough blood flowing through it (as blood carries oxygen to the brain).

The cure for this is so simple. A full body massage apparently does the trick.

I don't know if this could help you, but I think it worth a shot.

Hope this helps.