Low heart rate on citalopram?

Cardiovascular
Common (1% to 10%): Chest pain, hypotension, palpitations, postural hypotension, tachycardia
Uncommon (0.1% to 1%): Angina pectoris, atrial fibrillation, bradycardia, cardiac failure, edema (extremities), extrasystoles, flushing, hematomas, hypertension, myocardial infarction, myocardial ischemia
Rare (less than 0.1%): Bundle branch block, cardiac arrest, phlebitis, QT prolongation, torsades de pointes
Frequency not reported: Ventricular arrhythmia
Postmarketing reports: Thrombosis

https://www.drugs.com/sfx/citalopram-side-effects.html

Although hypotension is considered a common side effect, I suggest you inform your Dr. asap, so he / she can adjust the dosage of the med, or change the medication.
If you are concerned , not feeling well and as it is the weekend perhaps a visit to the ER would not be a bad idea as we both know, we are talking of a vital organ.