I don't know about later on, but right now it is definatley a physical thing. Each day has brought a new experience. Day One, I was just so tired from having been up for over 30 hours, Day two was ok, just a little slow, but I did wake up restless at 4:00am (46 hours into fast) which never happens. Day three brought me the worst cramping in my legs - started in my lower back, and here we are at day four. I arose early this morning - I'm usually pining for sleep, and have a hard time getting up early - I always do because my kids are early risers, it's just a constant struggle every day. Today I am up earlier than they are. It is hard to do anything without feeling like I may pass out. My heart is feeling pretty fast, and my limbs feel so heavy. I just keep saying "Do this one more thing and you can sit and rest." Also shaky. Oh, and I have had this cramping in my lower abdomen for 2 1/2 days, that feels alot like period cramps. So for me it is physical so far. I just hope those leg cramps don't come back. They were horrible. I might have overdone it yesterday too though because I had a lot of things to do yesterday.