I Awake, Whether After A Night's Sleep Or A Catnap,

I awake, whether after a night's sleep or a catnap, with a feeling of fear. The feeling is just that "a feeling", not related to circumstances or life situation and not related to dreams. What is going on in my brain to cause this ? It takes a few minutes to shake myself out of this and to reassure myself that I'm not crazy or need to be institutionalized. This has been going on every day for 4 years. My internist, endocrinologist and neurologist don't have a clue and have not been helpful. I really need to be pointed in a helpful direction.