On some noisy types communication is only possible wearing headsets and using the intercom. On quieter types, you will have one ear uncovered (the one nearest to your colleage) and will more than likely not use the intercom as you will be expected to be able to hear the other person. If you can't then you're going to get some strange looks asking to use the intercom all the time.
Your hearing may be bad or you may just have some temporary hearing loss. If you have had a recent cold or suffer from cattarrh then it is posibe they you hearing is better than you think, just reduced by some gunk in your tubes??