That's what I've found out about myself, anyway. When I'm working too hard and cutting back on sleep to five or six hours a night, I don't get reliable hardons as easily. It takes extra work to get the ol' cock totally stiff. That's not just after one night, but after repeated nights (and at times I'll go weeks without getting enough sleep). But when I can catch up on sleep and get at least seven or eight hours of sleep each night, I'm in good shape, and I can count on my penis to get and stay nice and stiff when I want him to (and even at times when I wasn't counting on him getting hard). I've been reading recently about how getting enough sleep is as important as eating right and getting good exercise. I'm a guy in my mid-to-early 50s who has been good about eating and working out for a long time, but there are times I suck at getting enough sleep. I'll bet I'm not the only one.