What are the differences between generalized anxiety, phobia, obsessive compulsive disorder and PTSD?

OCD is more like having intrusive thoughts, also feeling like one must repeat something multiple times till it's perfect or something bad will happen to them, etc. PTSD is caused by extreme trauma which can result in major panic attacks if a memory is triggered. Phobias are the intense, irrational fear of something usually very specific, such as snakes. People with phobias may go into a severe panic attack at seeing a snake safely behind glass. GAD (Generalized Anxiety Disorder) is classified as an abnormal amount of fear in everyday situations, restlessness, difficulty concentrating due to worry, heart palpitations, headache, etc. All of these disorders have a lot in common, however they have very distinct qualities that help differentiate them.