Extreme shyness can occur amongst people with severe mental illness. Some people become so severely anxious that it seriously interferes with their lives. When anxiety becomes chronic in social situations, it is often called social anxiety disorder.
Here are the symptoms of social anxiety:
anxiety about starting conversations
anxiety about being put ‘on the spot’ during school or college lessons
fear of being watched by someone
avoiding eye contact when conversing
avoiding or worrying a lot about social activities, such as group conversations
difficulty talking in front of people, even friends you know well.
anxiety about how you have performed in social situations in hindsight, possibly causing reactive depression.
intense anxiety meeting people you don’t know.
I used to be chronically shy and was fearful if put in any social situation, especially being put on the spot by my teachers. It is common in bipolar.
Here is more information: