All men without erectile dysfunction may have them and they normally occur around three to five times during sleep.
While it is not exactly known why NPT happens, there a few different theories proposed as to how or what causes it. NPT is associated with REM(rapid eye movement) stages of sleep.
One theory is that during REM stage of sleep, noradrenergic cells(neurons that release the neurotransmitter noradrenaline) located in an area of the pons called the locus coeruleus are switched off. It is thought that these cells are associated with the inhibitory tone of the penis; therefore, when their activity is reduced during REM sleep, testosterone-dependent excitatory tones can be expressed which result in an erection.
Also, Evidence supporting the possibility that a full bladder can stimulate an erection has existed for a while and is characterized as a 'reflex erection'. The nerves that control a man's ability to have a reflex erection are located in the sacral nerves (S2-S4) of the spinal cord. A full bladder is known to mildly stimulate nerves in the same region.
The reason for this NPT is that these exercises actually contribute to the health of a man penis. Erections causes the erectile tissue to swell which in turn oxygenates the tissue. This oxygenation maintains its viability and helps to prevent cavernous fibrosis, a condition that can ultimately lead to erectile dysfunction.
Another interesting theory is that erection during sleep prevents men from wetting the bed because it is difficult to pee with a hardwood.
So I guess it a good thing because it helps you keep your boner healthy. Be happy with your boner, its all for your own benefit.
