overdose with Magnesium?

I started out with 200mg of Magnesium and 200mg of calcium about 3 weeks ago and slowly went up to 500mg of magnesium and 500mg of calcium, I also take a bete blocker 10mg of Coreg, my pulse went down to the mid 50's and I was very lightheaded, do you think its possible its the magnnesium, I tried to stop the bete blocker but that was a bad experiment, I am on the lowest dose and stopped cold turkey and get palpitations, maybe I will take it every 36 hours and try to wean, any suggestions is greatly appreciated

Hi Razzle, thanks so much for your response, I will cut down dosage to 200mg and see what happens, I do think the Magnesium helped my tremors, I greatly appreciate the time you took to enourage me to try the Magnesium