Prostate Orgasm Dream?

I'm way before getting even P-Waves myself but strangely enough I have been half-awoken exactly how you describe three times already with low to medium P-Waves. And at least twice I was dreaming I was being gently stroked where I had the P-Waves (once my lower back and once my sex).
Maybe as we are fully decontracted while sleeping, the slightest erotic dream can trigger very easily a response, especially after an exercice ?

@WM59 @Kaly I am rewired and have a similar experience. Occasionally I wake up in the middle of the night and feel p waves. If I focus, this often leads to a wonderful prostate orgasm. My theory is too that it has to do with the fact you are fully relaxed when asleep. Combined with a certain level of rewiring and being able to let go this leads to an aless super o. Amazing when it happens.

So did I really have a prostate orgasm or was purely cerebral?

It is not an 'either/or' situation, a prostate orgasm can be induced by mental and physical stimulation, usually in some combined process. In your sub-conscious dream state your prostate orgasm may have been 75% induced by mental stimulation 25% induced by physical stimulation. When you experience similar feelings in your conscious awake state, your prostate orgasm will probably be induced by 'X'% physical stimulation and 'Y'% mental stimulation. While the feelings will be similar, they will not be exactly the same. Just as the source combination is variable ('X'% & 'Y'%) the resultant orgasmic experience will also vary.

A wet dream with a twist or perhaps even part of the rewiring.

It was both! Your wet dream may have simply been due to a natural 'pressure relief valve' being triggered 100% by physical stimulation (due to fluid pressure in the prostate) or a certain % may have been due to mental stimulation as well. The "...twist..." here was the aspect of temporary abstinence which may have contributed significantly to a pressurized prostate. All experiences interactively affect the on-going process of 'rewiring' and that 'rewiring' affects the mental stimulation %. So, your rewiring definitely influences your physical response and your physical response also influences your rewiring.

I think when I have a p-orgasm awake for the first time I'll know if I feel them again to confirm or deny that it wasn't all just a dream.

Yes, they will be similar but not exactly alike, so please avoid the trap of expecting them to be consistent. These feelings are going to vary as they are fractal in nature.
The Aneros journey frequently introduces men to an altered state of consciousness, a trance or dreamlike reality where one's subconscious is actively dominant and ego consciousness is only secondarily present. It is in this state the body's perceptual language and communication with our subconscious is most easily overheard by our ego consciousness. If the axiom "Nothing unreal exists" is true then the contrapositive would be "Everything that exists is real". Dreams exist therefore they are real. Confirming or denying what you experienced was in the context of a dream (an altered state of consciousness) may be missing the point of the reality of the pleasure actually experienced. You might find @Billy11 's Dreaming Aneros? an interesting read.
Good Vibes to You !

Sounds a bit similar to something I had. I haven't had a prostate orgasm yet so I don't have anything to compare it to, but I'd imagine what I experienced isn't too far off.

What happened was that I woke up in the middle of the night and started feeling pleasure waves. It was sort of like the feeling when you're really close to cumming, except much more intense. It feels like waves of heat radiating from around the prostate, spreading through the body. Each waves was stronger than the previous, and at some point it was intense enough that my whole body started to tremble. It was pure pleasure, not mind-blowing, but a state you'd want to stay in forever. Then all of a sudden I started ejaculating and all the good feelings disappeared.

I'd imagine what I felt was the build up towards a prostate orgasm, except it was induced by a wet dream. It was different from any other wet dream I've had, as I usually just wake up once I start to ejaculate, and not 15-20 seconds before like this time.