ED is a common condition in which a man cannot get an erection when wanted. Most men experience this at one time or another, and it can last anywhere from a few minutes to the rest of one’s life. This has two potential causes. One is physical. Perhaps the man has vascular troubles or has had an operation such as a prostatectomy that cut the nerves. The other, and more common cause is psychological.
Medical professionals have a nifty trick to find out whether the cause is mental or physical. They’ll have a man apply a ring of postage stamps around his penis before going to bed at night. Men without physical causes will have up to nine erections at night. If he has a nocturnal erection, the ring of stamps will be broken.