Here's my three-second mood improver: Think of a major positive event in your life. Imagine what your life would be like if it hadn't happened. Sounds silly but it works every time.
It doesn't sound sill it sounds to me like it would have the exact opposite effect. So I'm feeling low and I think "imagine if I'd not got my job, then I'd be feeling crap and be hungry and possibly homeless .. basically I'm an incapable and worthless person .. might as well top myself now".
In contrast I practice enjoyment of those things which make my life better, like dwelling on their benefits drinking deeply of the contentment a moment of happiness can yield.
Glad you've found something that works for you; and I'm going to dwell on that rather than imagine you hadn't and instead had become morose!