The true culprit
It seems it wasn’t my lack of watering that killed off my orchid flowers, but this icky white fluffy stuff.
I’ve found it on other plants, like my beloved pineapple plant, which I had to chuck out. I’ve cut the flower stalk off and scrubbed the leaves and stalky/rooty bits, and cleaned the area where the plant lives. Hopefully, it’ll recover and flower again.