Anxiety, feeling down and out, feeling unreal, and like my memory is slipping. then i started getting a little bit of a headache plus i'm tired. what could this be?

See doctor: See your pcp for exam/eval to rule out medical causes for anxiety, ?short-term memory problem, headache and fatigue. Write down meds you take (prescribed/OTC/supplements), any alcohol/drug/tobacco/caffeine use, any recent head or other injuries (I see you tagged "accidental fall" below) and current stresses to review with doc. Try to take it slower meantime. Best wishes.

Therapy needed: Such a chronic anxiety state and possible depression need help by a psychologist or psychiatrist(can prescribe medication as well). Stress management therapy and possible short term medication will result in resolution of your anxiety as well as the fatigue caused by continuing stress. Discuss getting a referral to an appropriate specialist with your physician.

Therapy?: Have you yet tried any form of psychotherapy? Typically, the optimal combination of things to treat emotional issues such as depression is medication (which, on your best day, is supposed to take the edge off symptoms) but the real gruntwork takes place in psychotherapist's consulting room.

These are classic: anxiety symptoms, of which there are about 33, en total. Sounds like they may be getting the best of you since they might be behind the derealization/depersonalization. Try treating the anxiety first. See a psychotherapist or psychiatrist. Here's a general reference on understanding anxiety: http://www.psychologyproductsandservices.com/page2.html

See below: You have to rule out medical causes first:i would recommend contacting your primary care physician asking for complete work up and take things from there. Meanwhile can start with psychotherapy to help you cope with your symptoms. Good luck!

Depression: First please get checked out for any physical illness. If you are OK, then it would be good to consult with a psychologist to help with these symptoms. Once you figure out the problem there could be medications that would help too.

Psychological issue: If you are worrying excessively or feeling down, it could be anxiety and/or depression. See a psychologist for an evaluation of the roots of your distress. Help may be a combination of psychological, biofeedback and medical interventions. Have your physician communicate with the psychologist for best results.