Hello and welcome!
Sorry to hear you are dealing with sleep issues/were awakened with a start. I know how this feels, and it is disturbing to be sure.
Is this something that only occurs at night? Or do you have challenges with anxiety whilst awake as well?
If this is strictly at night...then I would encourage you to explore sleep apnea...and possibly sleep paralysis as well through a sleep study. You do sound as if you could have symptoms common to both of these sleep issues...
...if you have trouble with anxiety in general...I would encourage you to seek help through your doctor if you've not done so already. You can discuss treatment options such as medication and/or therapy, to feel your best.
In either case...this link for self help in our Resources can help manage the symptoms you describe in your post. The 'Stress Relieving Exercises' are excellent at reducing the physical effects such as a racing heart. Learn and practice them, so you are ready if this happens again.
www.healingwell.com/community/default.aspx?f=9&m=104206Wishing you the best...and inviting you to post with us anytime for anxiety support!
S.C.