What Causes Shortness Of Breath And Light Headedness?

Question : Hello, I am a 29 y/o male ( 6 foot 2, 206 lbs) with c/o intermittent episdoes of SOB, light headedness, generalized fatigue and decreased endurance. I worked all day and I have been feeling the above symptoms most of the day, worse x last few hours. I checked my pulse and it was 46 bpm. I have had intermittent episode of bradycardia mostly noted at night when watching TV and sleeping (via my fit bit) in the 40s and 50s (checked this accuracy manually as well). This is the first time I have checked it during the day and it was this low. I have had this light headed/fatigue feeling on and off for a year now (worse today) with other symptoms including ( difficulty concentrating/cloudy headed/feeling out of it or having trouble thinking as quick as I normally do) and saw a neurologist in July 2015, with a nml MRI. Saw a Cardiologist in Dec2015/Jan 2016 with a nml echo and stress test. I know bradycardia is common in athletes and I am not one. Other possibly pertinent information includes I have had a recent 20 lb weight gain in the past year. I have pmhx of low TSH (thyroid nodules per US), intermittent HTN (not dx or on medication for either). The cardiologist I saw in January recommended I wear a 24/7 heart monitor for a few weeks to monitor these episodes. I have been holding off to see if sx improve. Today I am concerned because this is the first time I have felt these sx as severe and also noticed the bradycardia this low during the day while walking about. I Usually I notice the bradycardia at night while watching tv, and the SOB/light headedness feels slightly worse than normal. I am debating the need to go to the ER tonight or if I should wait until monday and just pick up the heart monitor (as I have had the recent echo/stress test in XXXXXXX that was normal, I don't know if this is enough information to ensure this is not a emergency and can be postponed until monday.) Any advice you can give will be greatly appreciated. Thank you!