Not just hallucinations but lack of sleep can change your very character and behaviour. The executive part of the brain in the frontal cortex becomes inhibited and you have less conscious self-control over the expression of emotions/feelings. You will become very noticeably irritable, angry, petty, quarrelsome and even sometimes violent.

I have had the misfortune of experiencing this twice in my life so far; the first on a month-long car trip with my buddy and the second while i was the caregiver/caretaker for my Mother. In both cases it was my lack of sleep which made me very difficult to be around.

1) Sleep Deprivation - https://en.wikipedia.org/wiki/Sleep_deprivation

2) Also Related; The medications that change who we are - https://www.bbc.com/future/article/20200108-the-medications-...

So whenever you note that somebody's behaviour has abruptly changed, always ask two questions; a) Are you sleeping well? b) What medications are you taking and what diet are you on?

While being partially conscious and losing a lot of cognitive function (spatial sensing, balance, short term memory)