Can taking 5, 000iu daily of vitamin d3 then stopping one day out of no where cause irregular heartbeat?

Not likely: Vit d is very long acting. It is stored in fat and liver and it takes a while to get deficient. Missing 1 day will have no consequence. The other conditions you list (anxiety, breathing difficulty, chest pain) certainly can be associated with irregular heartbeat. See your doctor.

Probably not: I would no think that stopping for one day or even several days would cause any readily observable problems if this problems persists you should certainly seek medical attention i do agree with the 5000iu /day as a good idea in general best wishes.