Sir Winston Churchill had problems with depression. I think I may be paraphrasing when I say he said "it was a visit by the black dog".
On the other hand, the "dog" of mania is more like a laughing hyena.
The main problem is this: no matter which one visits, you're either going to be nipped by the grumpy old black one or the hyena is going to rip off a couple of your fingers.
Either way, you're in "a world of hurt".