| Depends if it's underwater or during O2 admin as a result of suspected DCI.
Underwater remove the source (if possible), and help them out of the water (certainly wouldn't want to continue a dive, even if they appear to recover)! They may return to consciousness, they may not, but whatever just help them up and out (once safe to lift them, so not when they're tensed up). If you have a deco requirement then if they're still breathing and conscious then probably best to complete the deco, unless there are other more pressing concerns that mean you need to get them out of the water ASAP.
If the problem happens during oxy admin on the surface, then remove long enough to remove any symptoms of oxtox, and put them back on O2. DCI would be the primary concern, so keep the O2 on as much as possible while avoiding oxtox.
Obviously after any oxtox, wherever it happens or for whatever reasons, hospital treatment from professionals should be sought ASAP.
David |