Well done @porters, doing your occasional 10 day meditation sessions. Your metabolism was taking strain rising so early. The secret is to go to sleep early so that you get 7 hours sleep or more if you need it. Another secret is to not eat any meals too close to bed time. The digestion is taking much of the energy and at early hours of the morning may be draining you. Buddhist monks traditionally in some schools will eat their main meal at noon, and nothing after that at all. If you have low blood pressure it may be tiring, but your body adapts with continued effort and regulation.