A Government health website states the following
"When BGL's fall below 2.8mmol/L, brain function slows down, causing reduced concentration and response time, confusion, poor coordination, blurred vision, and can lead to unconsciousness."
That certainly used to be something like what happened to me. (apart from the blurred vision and unconsciousness parts)
However, since I started ignoring medical advice and doing my own thing I am much better off.
Last weekend, my heart was a bit faster and pounding a bit stronger than normal. Usually I would just eat straight away, but I decided to check my blood and got a reading of 2.3 (or 41mg/dl).
Instead of eating, I decided to play a game of lightning chess against Fritz with a handicap setting of 1.
Rules: touch piece, if the game takes longer than 5 minutes, or I fail to notice a check, I lose. No taking back moves.
Here is the game
Total game time was 2 minutes and 37 seconds. A pretty scrappy game, but I am no grandmaster and that is about as well as I play when my blood sugar is normal and I am making each move in a bit over 2.5 seconds average.
I checked my glucometer reading again after the game with my usual impeccable technique, and it read 2.3 again, so I ate some food, but much less than that same Govt website says one should.
Conclusion: No evidence of cerebral impairment at a glucometer reading of 2.3. How low does my blood sugar have to fall before my ability to play lightning chess is noticeably impaired? Stay tuned.
If you have diabetes, you really should learn the science behind avoiding brain fatigue when your sugar is low.