I'm a 32 year old female. My normal heart rate is between 55-65 bpm at rest. I have had these episodes, usually about an hour after drinking my morning coffee, where I will suddenly become extremely sleepy, lightheaded, and weak. I've noticed during these episodes my heart rate seems to drop, this morning it dropped to 43bpm, but I have seen it go as low as 38. I usually lay down and feel better after about an hour. When I feel better my heart rate goes back into the high 50s. After the episodes are over, I feel fine the rest of the day. This has been happening for a few years, and seems to be worst when I am heavily dieting. Could this be a reaction from the coffee, or something else?