I've no idea what that is, but I used to get this too. Particularly later in the retreat when dozing off at night. I'd just be drifting off and ZAP! Like white light and angry buzz / static all rolled into one.
Yes, that sounds like the same thing, but wow. Like whiplash. An interesting phenomenon, and hoping to learn a bit more about them.
With a schedule like that, exhaustion would be my guess!
They were quite different from exhaustion. There was dozing off, or near dozing off, plenty of times, but the blackouts happened only during non-drowsy sits. Of course, it's impossible to say for certain, because at that moment of blackout, there was no consciousness present to be aware of the blackout...
The blackouts were an expected outcome from my teacher, and the message I got from him was that longer was better. I didn't have direct control over them, but their length was proportional to how well my meditations were going beforehand. The most unique part was when coming out of them, I either felt silly / goofy / giddy, or just very tranquil and felt like getting back to business of meditating.
I'd be very interested to hear more about your practice Mike. In what tradition is your retreat? What is the "structure"?
The tradition is Vipassana, Mahasi lineage, equal parts walking and sitting meditation. Sitting is following the breath, and eventually moving concentration across a sequence of 30 or so points around the body. The 6-week retreats were in Thailand. A rather common / traditional retreat structure for over there. 4:30am wake, 6am meal, 10 am meal, then no eating solid foods for the rest of the day. Bedtime no earlier than 10pm, later encouraged. 12 hours of meditation per day, but more always encouraged. People generally start with 6 hours per day and work up from there. I found that 14 hours created a good rhythm. The momentum made it easier than doing just 12. There's nothing else to do anyway!
The last 3 days of the beginner's course is 72 hours with no sleep (3-day 'determination'). It is not easy, but at that point, I was only needing about 4 hours of sleep per night anyway, so there was not much sleep to let go of. It's mostly about staying in the present moment. From how I understand, it's not a test of endurance. It's more a way to ensure that sleep does not 'reset' all the progress that's been made while awake. The continuous practice is helpful to keep going further.
After that first beginner's course, you only do 10-day retreats, that each end with 48 hours of no sleep (2-day 'determination'). You can choose to do 3-day determinations, and some people do longer. So, the second time I went back for 6 weeks, I did one week+ warmup and three 10-day retreats with 2-day determinations, with some days of rest between.
I did zero studying and didn't know anything about jhana through both of those retreats. All I knew is what I experienced, with zero foreshadowing from my teacher at each turn. He kept reassuring me that everything was ok and expected. In a way, I feel lucky for that.
I started meditation to deal with manic-depression. It's gone! I had no idea there was so much more to explore. It's truly fascinating.