The half life of metoprolo is 3-4 hours. Meaning the drug reamaining in your system is reduced by 1/2 every 3-4 hours. The duration of it's effects is 13-19 hours. Get out your calculator and do the math.
You took a very small dose for a very short time, so you should be close to having none left in your body.
If you are still "feeling" effects after your "withdrawal," call your doctor and let them know. Not everybody metabolizes at the same rate.
Peace
Greenlydia