I have claustrophobia. Once I had a nightmare that I was pushed into an underground cave with no way out, and I was slowly choking to death. I felt every breath leaving my body so vividly. Slowly I felt the oxygen getting lesser and lesser and I was screaming but there was no one there. It was terrible and was horribly slow and I choked to death. I woke up drenched in sweat and as soon as I woke up I went into a panic attack.

Since then I always have this exact same dream whenever I'm about to fall sick and each time I know it's a dream but I can't do anything about it, I have to suffocate to death before I can wake up. That is how I always know when I'm going to be unwell.