Welcome to the site.
I am Dr. Kaushik and i believe i can help you with your problem.
Well it does seem like you have been dealing with depersonalization and derealisation issues all these years which to a greater extent have stemmed from a possible PTSD ( i.e Post Traumatic Stress Disorder) that started when you fell in the creek and feared for your life. Although a lot of time has passed by ever since you experienced your worst fear of dying many years ago but somehow the emotional setback ( PTSD) that you perceived then has still remained intact in your subconscious mind which every now and then comes to the fore into your conscious awareness in the form of depersonalization and derealisation.
So the crux of your problem is your underlying PTSD which eventually gives way to these two morbidities namely derealisation and depersonalization that you have been struggling with all along.
So I reckon in order to overcome these conditions you got to bring closure to your emotional baggage that traces back to your childhood traumatic memories and this can be done by using a combination of an anti depressant and counselling / therapy.
While Zoloft ( sertraline) at dose of 50-150 mg / day or Lexapro ( escitalopram) at dose of 10-20 mg / day can be the choice for the anti depressant, on the other hand as far as counselling goes CBT ( Cognitive Behavioral Therapy) is the best choice for dealing with PTSD and associated Depersonalization and Derealisation.
So now that you have tried so many treatment modalities so far I will urge you to give this above mentioned treatment strategy a genuine try. CBT is to be sought from a clinical psychologist while the anti depressant's prescription can be obtained from your treating doctor.
And I may add here that your memory problem finds it's roots from the unresolved co-morbid complex of PTSD and the depersonalization and derealisation , so while there is no harm in trying the medication as recommended by your doctor but please what is most essential is to put an end to all of this with a trial of the above mentioned strategy and to be on the same for at least 4-6 months to achieve full recovery.
Kindly discuss this with your doctor and try to reach a consensus on this and start the treatment as soon as possible and try to be patient with results as the drug therapy as well as counselling shall take around 3-4 weeks to start producing their positive outcome although full recovery shall be expected by the end of full course that amounts to the duration what I mentioned above.
I hope this helps.
Wish you all the best.
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