I would LOVE to get my 2 hours back in a day because of a last minute interview cancelation. The only person who would be truly irritated is the recruiter, who's job depends on meeting candidate quotas. Even then, they want you to be successful.

Trust me anyone reading this, if you are not feeling well, or something is distracting you, please, please, do feel free to reschedule your interview, even last minute.

Once you go through the process, and it's a no-hire, that is recorded in the system and you won't be allowed to try again for some extended period of time. At my company, it's 1 year.