Heart pounding/skipping beats

Not sure where to start, so I'll give some background info first.
I'm 53, 6' 3'' tall, 255 lbs. I've been taking Primatene tablets (Ephedrine HCl 12.5mg per tab) for mild Asthma since it was first released on the market approx 20? yrs. ago. I've been a heavy coffee drinker (15 - 25? cups a day) for longer than that. About 4 years ago, I started drinking diet pepsi and all but gave up coffee. Approx 2 weeks ago I noticed that when I'd go to bed and lay down, I would start to have an uncomfortable pounding heart beat that would beat 3 or 4 very hard beats and then seem to skip a beat. It was bad enough that I would eventually get up and wait for it to go away, usually in an hour or so. This has been almost a daily routine for the last 2 weeks. I remembered something I'd heard about "Aspartame", the artificial sweetener,
and since I was drinking 10 - 20 diet soda's a day, I looked it up and found out that heart palpitations were a symptom of aspartame toxicity. Today is my 5th day without a diet pepsi, yet the heart palpations persist. I did notice that over the 4 years that I was drinking the diet soda, my need for the primatene tablets went from very occasionally (1 to 3 tabs a week) to sometimes 2 tabs a day. Since I've stopped the diet soda, even tho it's only been 5 days, I've seen a dramatic decrease in my need for the primatene tabs. 3-half tabs in the last 5 days. I've started drinking 4 or 5 glasses of iced tea, unsweetened, these last 5 days. My question is, what is causing the very hard heart palpitations? There;s no accompanying pains, just very uncomfortable, pounding heart beat with the skipped beats. My caffeine intake is nil compared to a week ago, and the ephedrine that I've taken in the last 5 days is only 18mg's.  Is it a symptom of Aspartame toxicity? How long does Aspartame take to get out of your system? Should I go see my Dr. about this? I have noticed that I seem to have a bad taste in my mouth most of the time now, is this normal Aspartame withdrawals?
Sorry to go on for so long, but, being almost 54 years old, I'm starting to worry that this may turn out to be something very serious.

[curmudgen]

A quick read of your post reveals that you are taking ephedrine.  Ephedrine is a stimulant.
A side effect of ephedrine are palpitations.  I would suggest you do a web search - ephedrine and palpitations - and review the information.  Perhaps there is something else you can take for your asthma.  If palpitations persist the best advice always is to check in with your doctor.