Could well be - or just prolonged over-exertion instead of resting after an active day. I crashed for a week once after doing that, but was fortunate to recover to 'my normal'. Similar things happened again after prolonged over-exertion. It was always unavoidable exertion, e.g. scavenging firewood trying to keep warm, having to move things for builders and clean up their mess afterwards, and caring for a terminally-ill cat. I ended up very ill twice, taking at least 2 years after the last serious exacerbation to get back to 'my normal', I think. But it wasn't until after the second serious illness (which led to 4 days in hospital) that I realised what was causing it! (and of course no doctors did ). I had to work out and action the remedies without their help.