Bradycardia and Hypotension at night

34 year old female, with a recent EKG diagnosis of sinus arrythmia. For the past two weeks my blood pressure and pulse have been lower than normal (down to 117/72 from 130/80) pulse mid 50's during the day, low 40's at night. My concern is that they drop even lower at night (low 90s sys; 50 diast.).  Not necessarily while I'm asleep although when I do lay down flat they drop even lower, and even more so when I go into a relaxed state to go to sleep.  But I could be simply sitting down.

Could the sinus arrhythmia be causing the slow heartbeat?  I'm not in shape and I realize a lower pressure is beneficial. But it's a cause for concern because it's new, I don't work out, I didnt have sinus arrythmia before, and my pulse gets very low.  All cardiac tests and labs are normal. My cardiologist doesnt seem to be concerned about my low heart rate, although when I was admitted to the ER the ER doc didnt feel comfortable letting me go home with a pulse and bp that low  (88/50 pulse 47), so they admitted me, gave me fluids and let me go.

Now I have vague dizziness  even when my BP is reasonable.  Anyone else have this with an idea of things that could cause it?