I often wake up with a racing pulse. I can't think and I feel terrified. It takes me about an hour to fully calm down. I have no mental health problems that I know of, but this is really upsetting me. It this a symptom of a sleep disorder?
It may be a sign of a sleep disorder, certainly, and you'll feel better and have a better understanding of what's happening to you if you see your doctor about this. It sounds like you're describing something that's akin to a panic attack, such as Sleep Terror Disorder, which can be especially hard to deal with if you're feeling stressed or anxious. It may also be something that is rooted in your nervous system. Make an appointment with your physician. It may be the type of thing that is best diagnosed with a sleep study. In any case, you'll feel relieved (and probably sleep better!) having talked to a doctor about it.
In the meantime, here are some links you may find useful:
Sleep and Well Being: A HealthCentral Explainer
Sleep and Your Environment
Have you had any long term anxieties or long term stress that you have felt uable to deal with. If so maybe it's that that is disturbing your sleep.