This sounds a lot like episodes I used to have when I was little. I would suddenly jolt into awareness and become hyper-aware of my surroundings an external stimuli. Before this 'waking up', I would have seemed mainly normal, but really I think I was on autopilot. I was tested for epilepsy at the time after I told people about these occurances, but nothing came up. It now looks like what was happening was that during busy times I would just 'shut down' and zone out, but continue on autopilot until my brain had recovered enough to start coping with the external world again, at which point I would 'wake up' as if snapped back into consciousness. However, I'd still be able to function during my switched off state, just on autopilot. I don't know if that's anything like what you're describing, but it reminded me of it. It's something that still happens to me occasionally now, although less since I'll learned how to block/mute/lessen sensory imput so that it doesn't overwhelm me.
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