Walking slowly makes me tired

[PamNY]

Plus, in the specific case of museums and galleries, there's the fact that your brain uses something like 80% of the calories your body burns, and vision uses more than any other sense. Looking at stuff all day is exhausting - even if you're sitting down.

Very interesting replies. OakLeaf's comment might explain why I crashed while birdwatching. I do think I'll try some stretches or a bit of fast walking next time.

Not that I'm glad others have this problem, but at least it's not just me.

Pam