Sleepiness and depression are rare side effects of Atenolol, as this beta blocker (opposite to Metoprolol and Propranolol
) doesn't pass through the brain barrier in any high amount. But of course, a low blood pressure and slow heart rate may produce such symptoms, especially the first.
Yes, you are right that a slow heart rate can make PVCs worse.
You should ask your doctor what his opinion is. Anyone can try magnesium, it may help and it may not, it's impossible to say.