Could Fluctuation In Pulse Rate Of Heart Be Due To Dehydration?

I am 59yo female, taking Metoprolol 25mg 1Xday to slow my racing pulse. For last couple years my bp was around 160/80 (and sometimes a little higher) ish but last two or three weeks it has dropped to a much lower rate(about 100/59), but not much has changed in my life to cause that flucuation. Rather sedentary life, a little bit of asthma hay fever, dry air here in desert. Is it possible dehydration?