Do I need to give a reason for calling in "sick"?

I've got 25 sick days.

I want to use one of them as I have an interview for another job.

Do I just say "I'm not coming into as I'm not feeling well."

My boss is a sensitive & grumpy 35 year old woman. She gets annoyed at the stupidest things.

Do I need to give a reason for calling in "sick"?
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