To build on the comments of others Angelo, it is not uncommon after a day
of repetitive diving, and especially after several days, to feel
fatigued.  This is very common.  Some suggest that NITROX (gas, not John)
combats the feeling of post dive fatigue.  This is a very controversial
issue.  It is my understanding that no studies have substantiated this
claim, although there is much anecdotal evidence that NITROX helps.  I am
not certified NITROX  so cannot comment from experience.  I can tell you
that I commonly feel fatigue after repetitive diving.  It is typical a few
days into a dive trip to find oneself alone at the bar by 10
PM.  :(.  Also, I never sleep better than I do on a dive trip.

Dive safe,

/Don