How Long can a Person Go Without Sleep?

Currently the world record, although un-recorded by Guinness due to health concerns, is over 11 days. However, immediately after setting that record, it was broken by someone else who outdid him by 11 hours. But some chronic insomniacs have been said to go even longer than that, so that, on top of the health concerns, have caused Guinness to no longer record feats at sleep deprivation.