Depersonalisation and Derealisation are very common symptoms of spontaneous panic attacks and belong to a group of sensations/feelings often known collectively as Dissociation.
May I recommend the following book available from Amazon:
From Panic to Power: Proven Techniques to Calm Your
Anxieties, Conquer Your Fears, and Put You in Control of Your Life Paperback by Lucinda Basset.
This may help you if none of the recommendations in our resources works for you.
Kindly,
Kitt