I've recently watched Howl's Moving Castle (2004). When I was watching the movie, the changes in Howl's mood seemed really familiar to me, just like one of my near family members who has bipolar disorder.
The symptoms which attracted my attention toward this, were the multiple times that Howl seemed to be in an intense depression that even Sophie couldn't help him with, and just passing time would make him better. And when the depression is gone (with no specific reason), Howl entered a manic phase, in which (for example) he started to renew the entire house and became rather stubborn with his decision-making.
Is Howl intended to be dealing with any sort of mental disorder, specifically bipolar disorder?