The US Navy experimental diving unit conducted numerous experiments in the 1940s, in an attempt to try and gain a better understanding of central nervous system (CNS) oxygen toxicity. Luckily this clip survived to show what the poor "volunteers" went through.
The naval serviceman is shown having a convulsion through exposure to a high partial pressure of oxygen for an unknown time period. Compared with a warm, dry chamber, such a "grand-mal" seizure would normally be fatal to a diver underwater due to inhalation of water.
So technical divers need to be extremely careful when using hyperoxic mixtures to accelerate decompression. Basically plan your dive thoroughly, analyse and clearly label all gases, use gas switching procedures to ensure switching and confirmation of switching onto the correct gas at the correct depth, and pay attention to deco times and buoyancy on your deco stops.