The Causes of Erectile Dysfunction and Impotence
How to tell if your erectile dysfunction has a physical origin
As you may know, if your erectile dysfunction is more emotional and psychological in origin than physical, you are likely to be able to achieve a decent erection when you masturbate or during the night. But it is true that a few men will experience night-time erections even if they cannot get an erection when they masturbate.
An effective test for the absence of night-time erections is to stick a string of postage stamps around your penis when you go to bed. If the perforations have torn next morning, it's a reasonable bet that you had an erection during the night.
The presence of either night-time or morning erections tends to indicate that you have no physical problems with your erectile mechanism, so if you find that your erections are unreliable, that they either do not develop at all, or they come and go unpredictably, or that you do not get erect in response to oral sex, there is a significant chance that the problem is physical problem.
You should consider getting the opinion of a good urologist, but do not agree to a penile implant unless you have also seen a sex therapist and had some analysis of the emotional and hidden psychological factors which may be causing your impotence.