Hooray! It appears that the problem I have been dealing with ever since upgrading to Windows 10 on my HP laptop has been automatically resolved. I had only one problem with the upgrade; the fact that when I shut the lid of my laptop, it didn’t go to sleep properly, and I had to press and hold the power button in order to get it to turn off, and then boot it up from scratch, in the process losing all my running applications. I worked around it by telling my laptop to hibernate when I shut the lid, which sort of worked; it still didn’t shut down properly, but if I held down the power button and turned it back on again, it did at least keep all of my applications. I’ve just noticed (thanks to Windows 10 super stealthy updates, I didn’t notice immediately) that hibernation and sleep is now working properly. Current opinion of Windows 10 based on personal experience: fairly flawless.
Unfortunately, it turns out that isn’t the case. It’s not sleeping properly again. I think there may be some application that is preventing it from sleeping – I suspected Spotify for a while, but now I’m not sure. The investigations will continue, and in the meantime I’m back into hibernation mode.