Yes there are cruises from 2 days upwards.
If you want to cruise from uk and back look at NCL, P&O, Fred olsen or Royal caribbean, all offering various short cruises of between 2 to 4 night duration at various times throughout the year. You can also take short cruises with Royal caribbean to from Barcelona or Malaga or Oslo,& Norway etc.
If you want to go a little further, Carnival in the U.S. have 1160 two to five night cruises.
Try royal caribbean from southampton on the independence of the seas for four nights to ireland (cork) either in may or august, if its your first cruise you will be amazed on this ship, you can rock climb, ice skate or even surf board, we were on it last may, 2008, and found it absolutely fantastic.