I agree, I don't think to take it intermittently is a good idea. But how much are you taking and how low does your blood pressure go?
Taking Metoprolol now and again is not a good idea.
It would mean that now and again you do not have the protection from it that your doctor thinks is necessary.
Also after a heart attack, the beta-blocker is often prescribed not only for lower heart rates but also to avoid arrhythmias.
If the prescribed dose is too high for you, you should contact your doctor and discuss a lower daily dose or a switch to another beta-blocker.