Depression being the invisible beast is a pretty awesome interpretation. I didn’t even realize it when I watched it. I’m a survivor of depression and suicide so this episode tugs at my heartstrings.
I mainly came to this site, though, to ask a general time travel question and this episode is what triggered it. In the beginning of the episode when the doctor saw the monster in the painting why was he in such a rush to get to Vincent Van Gogh. It obviously wasn’t an issue of time. I think maybe that’s just the nature of the doctor? Definitely not trying to nitpick at the show because I love it.