have woken up around 5am a few times with my heart racing like I have been running/aerobics in my sleep. I do not remember dreaming of running. My breath is not labored. when I notice my heart is racing it comes back down, quickly just as it would while cooling down from an Aerobic workout. 30 years teaching fitness, aerobics, and yoga.
Hi. Thank you for your question. Heart racing during sleep is a known phenomenon. It happens during the REM (rapid eye movements) phase of sleep, a phase characterized by a flush of catecholamines (e.g. a Chat Doctor.  I am assuming it is a regular beat. My opinion is that no further investigation is warranted. I hope I was helpful. Greetings.