• Obtaining full erections at some times, such as when asleep (when the mind and psychological issues, if any, are less present), tends to suggest the physical structures are functionally working. However, the opposite case, a lack of nocturnal
  erections, does not imply the opposite, since a significant proportion of sexually functional men do not routinely get nocturnal erections or wet
  dreams.
• Obtaining erections which are either not rigid or full (lazy erection), or are lost more rapidly than would be expected (often before or during penetration), can be a sign of a failure of the mechanism which keeps blood held in the penis, and may signify an underlying clinical condition, often cardiovascular in origin.
• Other factors leading to erectile dysfunction are diabetes mellitus (causing neuropathy) or hypogonadism (decreased testosterone levels due to disease affecting the testicles or
  the pituitary gland).

• Diabetes and hypertension,
• Injuries (such as from prostate surgery),
• Side-effects of drugs (such as the protease inhibitors used in HIV therapy),
• Disorders (such as atherosclerosis) that impair blood flow in the penis
• Neurogenic Disorders (spinal cord and brain injuries, nerve disorders such as Parkinson’s disease, Alzheimer’s disease, multiple sclerosis, and stroke
• Hormonal Disorders (pituitary gland tumour; low or abnormally high levels of the hormone testosterone).
• Arterial Disorders (peripheral vascular disease, hypertension; reduced blood flow to the penis).
• Psychological causes: stress, mental disorders (clinical depression, schizophrenia, substance abuse, panic disorder, generalized anxiety disorder, personality disorders or
  traits), psychological problems, negative feelings.
• Ageing Lifestyle: alcohol and drugs,
• obesity, cigarette smoking (Incidence of impotence is approximately 85 percent higher in male smokers compared to non-smokers.; Smoking is a key cause of erectile dysfunction. Smoking causes impotence because it promotes arterial narrowing.
• Overtraining

A few causes of impotence may be iatrogenic (medically caused). Various antihypertensive (medications intended to control high blood pressure) and some drugs that modify central nervous system response may inhibit erection by denying blood supply or by altering nerve activity.

Treatment for Erectile Dysfunction-ED