system
Given the following post, respond as if you're commenting on Reddit:
human
[Doctor Who] What do the psychological and mental changes of regeneration feel like?

Let's say that I start regenerating into my next 'incarnation'. Obviously, I'm going to look different, but what of the mental and psychological changes? 

If I loved apples before, while I regenerate would that instantly 'reverse' to hating apples? Would what I was thinking during regeneration change, in terms of feelings and mental processes? Would it be like flicking a switch? Would a stranger I met and thought to be cute suddenly seem to be average in my opinion?
gpt
Whilst the Doctor is a bit of a unique case, you kind of have to base it off them.

(Going from Doctors 9-12, as I've only seen the new series) There is a retention of memories of people and places, and general ideals/mannerisms (see also the Master), but each Doctor has a unique level of flair; whilst The Doctor is always eccentric, they will deal with problems slightly differently, and have unique perspectives ("What you do in your regeneration is your business" or some such in a crossover episode). 

It also takes a bit of time (a couple of days generally) for The Doctor to return to full mental and physical health, and will be disoriented for that time and relatively weak. Though the change to the 'new you' takes place immediately.

The start of 11's run showed that tastes change after regeneration (sorry, it's possible you will hate apples now), however their opinions on people relatively stayed the same, and they will still be attracted to the same people (9-10, 11-12) (that person will still be cute in your case, hopefully they're still attracted to you).

Overall, it's quite a dramatic change in  unique mannerisms, but there's a retention of the same base, most memories, and relations with people. These changes are basically immediate, but it will take them a few days to get out of the disorientation and back on the feet.