It's an interesting feeling. It's like all the typical cognitive/social filters we view life through are removed and you can see reality for exactly what it is.
It's also terrifying because you can come to some fairly serious realizations in a short period of time before those cognitive/social filters slam back into place. The best way to avoid this is to not think about anything too serious. However, sometimes you can't help it because your brain has things on the backburner and it takes it as an opportunity to make you think about such things. You can't always trust your brain.
PNC usually only happens after at least decent sex, bad sex or one just spending some time with themselves does not usually produce PNC. The better the sex the more likely PNC is.