I’m pretty sure everybody has these days from time to time; when your brain inexplicably becomes your adversary and has you lose all confidence in all that you do.
Normally this happens when you’re tired for some reason. While I was on my own running the length of the UK, I would often wake up in the night with terrible anxiety about what I was trying to do. Then I would wake up in the morning and be 100% confident again. Strange.
I don’t know whether it is exclusively down to being tired, or possibly being subconsciously overwhelmed by your environment without realizing, and tiredness then brings that to the forefront.