Decompression sickness is a condition precipitated by rapid changes in the ambient atmospheric pressure, mostly in rapid ascent from underwater but can also be from rapidly reaching high altitudes in jets. Onset is in 30 minutes to 6 hours after decompression. It occurs because at high atmospheric pressures (such as when one is several hundred feet under water) the blood can contain more dissolved nitrogen than at lower pressures; when the diver ascends rapidly, the blood can no longer contain this dissolved nitrogen and tiny gas bubbles begin to form in the blood. Symptoms include: body pain (mainly in the joints), headache, confusion, itchy skin rash, visual disturbances, weakness or paralysis, dizziness or vertigo. The condition can be fatal. Compliance with the schedules set out in dive tables may lessen the chance of decompression sickness.