Is it normal to sometimes feel sad for no real reason?

I'm not depressed, normally I'm really happy but today I just feel a bit... down hearted? I should be happy - I may get Invisalign soon, I've just finally finished my coursework for A level and have been told I'm gonna get a good mark, etc... Is it okay to sometimes not feel happy for no... show more I'm not depressed, normally I'm really happy but today I just feel a bit... down hearted?

I should be happy - I may get Invisalign soon, I've just finally finished my coursework for A level and have been told I'm gonna get a good mark, etc...

Is it okay to sometimes not feel happy for no reason ? :/
Update: I'm 17, I guess I'm still a teenager lol :)
But it's nowhere near that time of the month, thank god haha
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