One of my close friends suffered paranoid psychosis for months, literally every single day, 24/7, she'd be walking around, going to work, making dinner, etc. utterly convinced that "They" were watching her, that her every text and email was being read, all her online activity was being monitored, and the same person reading all her texts was watching her in real time via CCTV whenever she left the house. She was completely functional, just 100% convinced that this group of people in authority were watching and monitoring everything she did.
She used to turn up on my doorstep whenever she needed to google something she didn't want "Them" seeing (she couldn't phone or text, otherwise they'd know that we were friends, and start subjecting me to the same level of monitoring).
She refused to believe there was anything wrong with her, in her mind it was undeniable and logical that of course the authorities were spying on her 24/7. In the end she was only hospitalised because of the stress and the actions she was doing to avoid them seeing her, like walking miles to use rural payphones. She was clearly not quite right in terms of doing odd things, but she still managed to wake up and commute to work every day.