l was diagnosed with a cardiac arrhythmia a while back, and a slow heart beat which runs at around 63 bpm. l know 63 bpm isnt that slow, but thats only for athletes and stuff right? So, can a slow heartbeat cause a person to be down and sad all the time?

Knowing you have an arrhythmia can make you down and sad. This is a hb within normal range. Anything from 60-100 is considered normal. Mine varies from 60-90.

The down and sad could possibly be a thyroid thing, or a mindset thing, or a hormone thing. Chuck Swindoll has a good book on attitude that may give you some encouragement.