My son as a child was a generous happy child and would always offer you a sweet, anything he had actually.
Then as he became ill, he became so selfish, one night he had a huge family bag of doritos and he wouldnt even give me a single one lol.
Now on meds for a year , he has totally changed, he offers, If I ask he always gives me a little, shares, I don’t ask him all the time, for instance I made him some pancakes for his breakfast (lunch time) they looked so nice so I asked him for a tiny piece of one, he willingly cut me a piece off without a word. Rewind two years and he would have flat refused or kicked up such a fuss.
I just thought there it was something I noticed, did the illness make him angry and greedy and only think of himself, yes I think so.