Answer to Question 1
Obsessions are repetitive, unwanted, intrusive thoughts or images or impulses that may seem silly or crazy, are anxiety-provoking, and are resisted strongly but unsuccessfully. Compulsions are repetitive behaviors or mental acts that are used to reduce anxiety, especially the anxiety associated with the obsessions, and that do not produce any pleasure. Most patients with OCD show both obsessions and compulsions, but this is not necessary for the diagnosis. The person must recognize that the obsessions or compulsions are excessive or unreasonable. What's more, the thoughts must not be simply excessive worries about real problems. Most normal people (80-90 experience obsessive thoughts at times. Research suggests that the difference between normal obsessions and clinical obsessions is a matter of degree. In most cases, it would appear that the obsessive thoughts come first and that the compulsive behaviors are often an attempt to cope with the anxiety provoked by the obsessive thoughts.
Answer to Question 2
(1) A phobia is a persistent, irrational narrowly defined fear that is associated with a specific object or situation. (2) In contrast to a normal fear, phobia involves attempts to avoid an object that others do not find dangerous. (3) A person who fears cats may prefer not to be around them, and may show physiological arousal when close to a cat; a person who is phobic of cats would have an immediate fear reaction upon seeing a cat, and the person's attempts to avoid getting closer to the cat might interfere with whatever the person was doing at the time.
Blue whale skeleton at the Canadian Museum of Nature in Ottawa, Ontario.
Skin signs are objective evidence of an illness or disorder. They can be seen, measured, or felt.
Obsessive–compulsive disorder.
Nature
DSM-5 Criteria for Substance Use Disorder
Classification of Antidepressants: Treatment of Major Depressive Disorder