Are Unforgivable Sins Real?

The notion that there might be a sin or sins that are absolutely unforgivable, even by a bishop, is pretty terrifying. Given what the Church teaches about the sacrament of confession and reconciliation, it’s hard to see how a priest or the bishop wouldn’t be in a position to provide some way back to God. What’s more, isn’t baptism, the originating sacrament of faith, supposed to be able to cleanse all sins? A clean slate? A totally new beginning?