Tiredness, public transport, airplanes and awful food are all legitimate reasons to get a bit grumpy when travelling, so this is what I put it down to. About 4 days into Japan I realised I was completely wrong. We went into the first cafe since we arrived that understood English Breakfast Tea with a separate little jug of milk. We brought teabags of our own of course, but you can never get milk and there usually isn't even a kettle. Lots of places serve tea but almost never English Breakfast, or anything close.
I drank the tea and my mood elevated so much that I started to worry about real tea addiction. My nagging background headache disappeared and I swear my feet didn't even hurt as much.
We now prioritise finding English Breakfast Tea over everything else. I see this being problematic on the Indonesian jungle trek.