Question) How many cups of coffee is it okay to drink a day?

I love coffee and drink several cups a day, but I'm curious about the appropriate amount for my health. Some days I drink two or three cups, and on days when I'm tired, I drink more. However, I sometimes feel my heart pounding or have trouble falling asleep, so I'm worried. I understand that the appropriate amount varies from person to person, but I'd like to know what level is generally considered safe. If anyone has experienced improvements after reducing their coffee intake, or has established a recommended amount, please share your advice.