Before you run out to dry clean your suit, take another look at your subpoena. There are two kinds of subpoena, and one does not require a court appearance.
A subpoena is a legal command with threat of punishment if you do not comply, but don’t panic. The subpoena ad testificandum is a lovely formal court invitation for you to appear and testify. That one may need some preparatory work on your part and that of your lawyer and tailor. The subpoena duces tecum, however, is generally a request for documentation and doesn’t necessarily entail a trip to the hairdresser’s.
Either flavor of subpoena may be delivered by a variety of servers, from an innocuous piece of registered mail to a sheriff’s deputy. The important part is to respond. Subpoenas can be postponed and even objected to. Acceptance of a subpoena doesn’t necessarily obligate you to comply, but you must make your objection known to the court.