This morning I walked 4 miles. Temperature in the 90s. Then I mowed the lawn. Then I did P90X yoga for and hour and a half in air conditioning. With about 10 minutes left of yoga, I have no memory of completing the yoga, yet I apparently finished and then went to the garden to pick some vegetables. There was about a 15-20 minute period in which I was functioning, but I don't remember. What could cause that?