Why did my Apple Watch Series 6 ask me to “Turn Digital Crown to unlock” when I’d been nowhere near water?

I have a new Apple Watch Series 6. It’s very nice.

Last night, before going upstairs to bed, I looked at it, and it was blank. I thought maybe it had run out of battery so I tapped it and a very (and I mean very) faint image of the time appeared, but it was not my clock face – it was just the time in large (very faint) numbers in the top right. I tapped it again and a (very faint) icon and a message appeared, and then disappeared after about a second or so. I tapped it again and the same happened. The message was so tiny, so faint, and so brief that it took me about five or six minutes to finally read it. It said, “Turn Digital Crown to unlock watch” (or something similar).

Searching for this message returns result after result about ejecting water, but the message said nothing about water, I don’t remember a “water drop icon filling up” as I rotated the crown, and I don’t remember any tones playing (which is how I think the water is ejected). Also, I’d been sat on the sofa for most of the evening – nowhere near water. Rotating the crown restored normal functionality (and I didn’t have to enter my passcode).

I’m confused for two reasons:

  1. because I don’t know why it was locked
  2. because the message was so damn hard to read.

This second is baffling me. The message was so faint that I had to turn off all the lights in the room to read it, and even then it was so small that I could barely read it without my glasses (which I generally only wear for VDU work). Given that there was nothing else on the screen, why would an important message like this be so small and difficult to read?

I imagine this might have been something to do with my Bedtime (Sleep Schedule) settings in my phone, which would have activated by this time, but I can’t find any information on this because every search result I find keeps talking about water!

Any idea what was happening?