Wow, sxyporkie, you look a lot younger!
As for caffiene, contrary to popular belief, caffeine actually slows down your heart rate if you drink a cup of coffee. It's been well documented in many experiments. So, why do some people get palpitations? They're just more anxious which causes them to release more andreline causing the heart rate to go up. If you consume more than two cups of coffee, then the heart rate will start to get higher.
Caffeine in green tea is not significant. Also, green tea contains theanine which is believed to counteract the side effects of caffiene. That may explain why people feel "relaxed" after having a cup of tea.
Caffeine is addictive, phsyically and mentally. If you stop taking it, you'll have physical withdrawal... headcahes and tiredness. Mentally, you'll feel less alert and more foggy.
Caffeine, despite being a stimulant drug, remains one of the safest drugs to consume thanks to its huge safety margin.