"Do not be sad!"

Translation: दुखी मत हो!

[i8hail]

Why is it ho and not reho, from rehana

[vinay92]

दुखी मत हो! - Don't be sad - from होना - 'to be'
दुखी मत रहो! - Don't stay sad -from रहना - 'to stay'

[U7K7atnO]

I believe because you are telling them to be something not remain or stay something. Also, my understanding is that rehana is like a helping verb and isn't the only verb in a sentence often.

[yhagood]

Why is मत after दुखी? and why use हो?

[vinay92]

The negation मत should be adjacent to the verb हो. दुखी is an adjective.