Heart skips for no reason. Had an ekg, but just an 'irregularity.' is there something else going on? Sometimes wake up to racing heart (+/- 160 bpm)
Possible SVT or Afib. The most common arrhythmia in someone young is supraventricular tachycardia (svt) in older people atrial fibrillation is a common arrhythmia that can show up as you described. I'd recommend a 24 or 48 hour holter monitor if the feelings are frequent, however if the tachycardia is infrequent a looping or non-looping event monitor may help diagnose the arrhythmia.
There are reasons. You may have an arrhythmia which may be entirely benign or a marker or harbinger of something more significant. This is not the format to ascertain cause other than to recommend you see your doctor to start the appropriate evaluation; a good history, exam, some blood work, ecg, possibly a heart monitor, echo, stress test. Leave it up to your doctor.