Journée étrange, mais pas désagréable. Je vais passer la nuit au bureau.
We'd usually say "une bonne journée" (a nice/good day as opposed to a beautiful day).
As for being
malheureux, that's a little harder. No problem with grammar at all, but it seems to me that we often use euphemisms instead, like « Je ne vais pas très bien » (I'm not doing very well) or « Ça pourrait aller mieux » (It could be better). « Je suis malheureux » is correct, but if you say it to a native, they'll probably think "Wow, is his life going
that bad?". I don't know why, but we seem to take « malheureux » more broadly and apply it to a whole period of one's life, whereas being sad in English can be just for a few hours.
« Je suis triste » sounds less permanent I think, although it doesn't mean quite the same. I guess the key here really is euphemisms. How are you going? Going well, going bad (Je vais bien, mal). I'm sad, but it's okay (Je suis triste, mais ça va passer). I'm feeling down ever since my wife left me (Je suis malheureux depuis que ma femme m'a quitté).
Again, I bothered with more details than necessary, and nobody would have a hard time knowing exactly what you meant. Those tips are just to sound more natural
