Is a drop in heart rate normal?

Heart rate: Heart rate is normally variable. A modest drop in rate is not a cause for concern. A large drop which causes dizziness or other symptoms should be investigated.

Heart rate: Heart rate normally varies depending on supply and demand for cardiac output. Drugs, conditioning and other things can also cause heart rate change up or down.

Heart rate: Heart rate normally varies through the day. There could conceivably be abnormal drops in heart rate but you don't provide enough information to speculate.