Psychosis (also called a psychotic experience or psychotic episode) is when you perceive or interpret reality in a very different way from people around you. You might be said to 'lose touch' with reality. The most common types of psychosis are hallucinations and delusions. You might also experience disorganised thinking and speech.
Paranoia is thinking and feeling as if you are under threat even though there is no (or very little) evidence that you are. Paranoid thoughts can also be described as delusions. There are lots of different kinds of threat you might be scared and worried about.