What they actually are
They have nothing to do with dreams, and nothing to do with needing to urinate — which is the folk explanation and is simply wrong.
During REM sleep the balance of the nervous system shifts, and the same machinery that produces an erection during arousal fires without any arousal being involved. A healthy man cycles through this three to five times a night, each episode lasting twenty to thirty minutes. Waking during or just after the final REM period is why the last one is the one you notice.
The useful part is that this happens with the brain switched off, so to speak. There is no performance, no partner, no expectation and no anxiety anywhere in the loop. It is the nerves and blood vessels running the process unsupervised.
Why that makes it such a good clue
Erectile dysfunction is a failure of one of four steps: the signal from the brain, the nerve pathway carrying it, the arteries opening, or the veins closing to hold the blood in.
A nocturnal erection tests the last three of those without involving the first. So if the hardware works reliably at 5am but not with a partner at 11pm, the hardware is not the problem — and no amount of investigating blood flow is going to find the answer.
Reading the pattern
| What you are seeing | What it points towards |
|---|---|
| Still regular and firm, but difficulty with a partner | Psychological, situational or relationship factors. The physical machinery is intact. |
| Faded gradually over several years, alongside gradually worsening ED | Vascular — the most common picture after 50, and the one that warrants a cardiovascular work-up. |
| Stopped fairly abruptly around a specific event | Often a new medication, a life change, or the start of an anxiety loop. Check the prescription list first. |
| Present but noticeably softer than they were | Early or partial vascular change. Worth acting on now rather than waiting. |
The gradual-fade pattern is the one that deserves the most attention, because it is the one most likely to be telling you something about your arteries generally rather than your erections specifically. Why that connection matters.
Four reasons it can mislead you
This is a clue, not a diagnosis, and it is wrong often enough that it should never be the only thing you go on.
- Anything that wrecks REM sleep suppresses them without any erectile problem existing. Shift work, insomnia, a new baby in the house, and a late night all qualify.
- Alcohol in the evening reliably suppresses REM in the first half of the night, which is why a heavy weekend gives a misleading reading.
- Untreated sleep apnea fragments REM badly, and separately harms erectile function — so it can produce a physical-looking picture that is really a sleep problem. The sleep apnea link.
- Waking naturally versus waking to an alarm. An alarm frequently pulls you out of a non-REM phase, so you miss the episode entirely. Weekend mornings are the more honest sample.
How to observe it properly
If you want to take something useful to an appointment rather than a vague impression, spend two weeks on it.
- Note simply whether one was present on waking, and roughly how firm — none, partial, or firm enough for penetration.
- Record it on waking, not later in the day. Recall degrades quickly and skews pessimistic.
- Note alcohol the night before and roughly how well you slept, so the poor readings can be interpreted rather than counted.
- Include at least three or four mornings where you woke without an alarm.
Two weeks of that is genuinely more informative than the questionnaire most online services will ask you to fill in, and it takes about five seconds a day.
What replaced the stamp test
The old trick of wrapping a ring of postage stamps around the shaft overnight to see whether it broke was a real diagnostic method, and it worked on the same principle. It has been superseded by devices that record both rigidity and duration across a full night, which a sleep or urology clinic can arrange.
In practice, formal testing is now used fairly rarely — mostly where the cause is genuinely unclear, or where it matters legally or for an insurance claim. For most men, the two-week home observation gets to the same answer.