Maybe it was the Melatonin in the blood
Lowers blood pressure
The pineal hormone, melatonin (N-acetyl-5-methoxytryptamine), shows potent receptor-dependent and -independent actions, which participate in blood pressure regulation. The antihypertensive effect of melatonin was demonstrated in experimental and clinical hypertension.Oct 8, 2014
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4227197/