heart beat randomly slowing down?

over the last 2-3 days i’ve noticed my pulse will be normal and then suddenly drop and go bum……bum (as in one heart beat) and i’m so scared??? this has never happened before and trust me i am a chronic pulse checker. it’ll go from bum..bum..bum.. to bum………bum…bum……….bum. and google is no help. nothing online sounds like what i’m experiencing. i don’t have any other symptoms that accompany this either. no dizziness no nausea no lightheadedness. basically my heart starts beating super slow out of nowhere. i’m a heavy smoker (i vape) and a moderate drinker.