As for why it happened, well I currently have a very bad cold and it might have affected my co-ordination. Both times, I was holding the mug in my left hand (which is a risk even when I'm at the peak of physical fitness), and my grip slipped when I caught them on the shelf.
I haven't tested myself for COVID-19 because I don't think that's what it is — it's just a bug that's going around. My younger daughter caught it (a lot of sick people go into pharmacies). She told me she felt the symptoms coming on when someone else described them to her; weirdly, as she was telling me this, I could feel the symptoms coming on myself. It was too quick to have picked it up off my daughter; I think I must have caught it from Colchester.
Despite being in close contact with both of us, my wife is unaffected. She almost always escapes colds. I think they're afraid of her.