Is it normal to be inexplicably depressed?

You're not at all weird.

Its actually common, more so than people realize or care to admit. People can have depression and still be well adjusted. Depression isn't solely limited to the stereotypical mopey, hates life type of person. It can be a blah feeling. You're still normal. You should reach out. It would help. Repressing your feelings increases internal tension, raising cortisol. That's a physiological effect. Since you mention two factors that can make someone feel physically blah, yeah. There are things you can do to change whatever is going on internally to uptick your feeling of neurochemical contentment. I am not one of those crackpots that thinks depression means someone is sad, or needs talk therapy, or needs instant medication. Sometimes, you feel blah like "winter blues" (Seasonal Affective Disorder). Its probably not even a disorder, more of a common cause of low sunlight exposure (just increase time in the sun, or Vit. D and problem is solved). The medical world goes a tad bit overboard with turning everything into a profitable disease. But, the research yields ample reasonable evidence that makes me think its real. If you do think you match the characteristics of SAD, or even depression, you can get longer exposure to full spectrum sunlight, you want more vitamin D, an increase in omega 3 fats, and other things. You can do this if you think you're depressed or not. Its all good for optimal health. :-)

If you're really curious? Look up this book titled Why Zebras Don't Get Ulcers by Robert Sapolsky.

If you want to watch an entire lecture on this? Here you go...This could bore you, lol! I don't know. I thought I will drop the link anyways. :-)

Stanford's Robert Sapolsky On Depression
https://www.youtube.com/watch?v=TIcf-2AFHgw

This lecture below is really easy to follow. He kind of talks like he's going off on religious zeal so use your thinking cap and watch it anyways. Maybe his zeal is from the pure enthusiasm he feels for his research findings. Its all stuff anyone can apply. All he advocates is lifestyle modifications that give your body a healthy boost.

Depression is a disease of civilization: Stephen Ilardi at TEDxEmory
https://www.youtube.com/watch?v=drv3BP0Fdi8

Only reason I agree with Ilardi and Sapolsky? If I eat junk, miss sleep, drink soda, or work too long, I feel essentially physically 'depressed'? I'm not sad, just blah. Lots of people feel like this and don't even realize it. I end up feeling like someone with chronic fatigue. Fortunately, I can get rid of it. If I don't eat junk? I feel REALLY GOOD. An omnivore fresh foods diet keeps me in excellent health. I have no chronic health issues whatsoever.

Hippocrates — 'Let food be thy medicine and medicine be thy food.' <-- It's true in my experience.

You're not wierd this is normal I hope u feel good soon

Depression can effect anyone at anytime if their life even at a good point in their life x