Yes, 40 is a little low for a normal person not on beta-blockers. Is it a true 40? Take your pulse for a full 60 seconds. If you do not become light-headed upon standing, then I would not worry about it because your stroke volume is adequate to perfuse the big nerve in your head. Of course, if you are worried call your doctor, etc.
(Insert usual disclaimer about this message not being intended to treat, diagnose, etc.)