So, to expound on the BOE... If you pay attention - really pay attention - to the behavior of a penis, the length and girth expand a bit fairly often during the day. During waking hours, we get itty-bitty semi-hard-on's.
This is blood flowing into the Cavernosum - the chambers in the shaft which, when full, create an erection.
You can see the veins and arteries along the outside of the shaft,
but the cavernosum don't have the benefit of these for a constant supply of blood oxygen. The BOE makes up for that lack of steady blood supply.
Of course, during puberty, with our raging hormones, we'd get hard-on's out of the blue. Didn't matter what we were doing...A contributing factor during those years was the burgeoning boner rubbing against clothing and BAM! our cock is standing at full attention, sometimes even leaking pre-cum.
And we noticed. Boy, did we notice!
But as we move beyond puberty, not only do the hormones level out, we stop paying attention to the slight tumescence as it happens and we typically don't get fully hard.
The difference with nocturnal BOEs is that at night we are completely relaxed, our minds are not pre-occupied with other things like work, dropping off or picking up the kids, the chores that need to get done around the house, school studies...the erections are free to develop full and hard. Particularly during REM sleep. And they can last longer - as long as 30 to 90 minutes.
May you notice your numerous BOE boners this weekend, guys, and enjoy them.
And, may those in the path of Hurricane Matthew batten down the hatches and be safe.