All men experience temporary periods of impotence at some time in their lives, and these need not cause alarm.
Impotence is a man's inability to produce, or maintain, a penile erection.
For this reason, an impotent man cannot have sexual intercourse. Medical specialists define impotence as the persistent inability to achieve an erection of the penis. During a single night, most normal men will experience several periods of erection lasting for a total of one to three hours. When investigators checked impotent men during sleep, they were surprised to find that half of them experienced erections. The occurrence of erections during sleep was almost always evidence that a man's physical erectile capacity was intact.