The latter is a manifestation of excessive shyness, which leads to anxiety in social situations. The former is characterized by pervasive worry not justified by life circumstances. Obsessive-compulsive disorder requires a bit more explanation. Obsessions are recurrent and persistent thoughts that cause marked anxiety or distress. An example is a person who keeps thinking that his hands are dangerously contaminated with germs.
Compulsions are repetitive behaviors or mental acts done to prevent or reduce anxiety.
An example is the previously described person who may then wash his hands 100 times per day. Anxiety disorders usually need treatment because they cause significant suffering. Unfortunately, there are many who self-medicate with alcohol which frequently results in further problems. Two better solutions are counseling and prescription medication. Counseling can help the sufferer to gain insight into the causes of his or her anxiety.