How can doing Communion unworthily cause damnation to your soul?

Tomorrow at my church, we’re having a New Year’s service and after the service there’s going to be communion. Wednesday, my pastor said to examine yourself because if you don’t, you’ll cause damnation to your soul, he also said you should stay home because if you do drink take it unworthily, he doesn’t want you to bring damnation to yourself. I was wondering, what does he mean to ‘examine yourself?’ To repent for all your sins or something else? And how do you make yourself worthy? I don’t want to do anything wrong and be damned eternally because I didn’t do it the correct way.