Reminds me of my early-morning driving lessons. No matter how much I prioritized being rested for them, on the morning drives my attention was always 60%+ focused on just not falling asleep. Several times I had a situation when I would suddenly realize I've been asleep for the past 5+ seconds - while going down a road at 100km/h. The fear of this resulting in an actual accident is a major factor why, after random life circumstances interrupted my learning, I haven't pursued that license again.