out of sorts

out of sorts (slightly ill, upset, or unhappy) — не в духе, не по себе

If you are feeling a bit upset and depressed, you are out of sorts

Example 1: ‘How are you?’ — ‘I’m feeling a bit out of sorts; I’ve been feeling a bit out of sorts lately.’

Example 2: ‘You look a bit out of sorts today’.

This means that you don’t feel right. You are not necessarily ill but you don’t feel 100% or you don’t feel your normal self.

The idiom can be used as an excuse for getting impatient, annoyed, or mad at someone inappropriately. It's more like being in a bad mood.

Example 1: Sorry I snapped at you — I'm really just out of sorts today. Forgive me?

Example 2: "Why are you so out of sorts today? You're finding fault with everybody. Did you get up on the wrong side of bed?" (another expression for being in a bad mood for no apparent reason.)

in the doldrums (inactive; very quiet or dull; in a low or undynamic state) — не в духе; хандрить, быть в плохом настроении:

Example 1: The financial markets have been in the doldrums for several months, pending the outcome of the world trade negotiations.

From sailing:
The Doldrums is the name given to the area of the ocean near the equator where the tradewinds tend to neutralise each other (экваториальные штилевые полосы {мор.}).
A boat was in the doldrums when it was becalmed and there was no wind. Ships’ crews were sometimes psychologically affected by this condition.

flat lining
tread water