Are there any differences in the meaning of or when we use the idioms ‘out of sorts’ and ‘the doldrums’? The definitions in the Cambridge Dictionary are:
Doldrums is not a common word. “Out of sorts” is more common.
I would expand on both definitions. Neither one is restricted to being unhappy or sad. They are both vague ideas that can be used in different ways. So the difference between them is more a choice of words rather than a fixed difference in meaning.
“Out of sorts” can be used for almost any negative feeling. It can be used for feeling sad or unhappy. I think it’s more commonly used for feeling mildly unhealthy. It is non-specific and vague. It can be a combination of being tired, slightly ill, less alert, etc. The important thing is that it is non-specific and mild.
Doldrums is much less common. To me it has a similar meaning as “out of sorts”. But the word is so uncommon I don’t know how it’s normally used.
Doldrums is also used by sailors to describe the weather patterns near the equator. The old sailing ships might be stuck in the doldrums with no wind.
I would probably oversimplify it as follows:
Doldrums: No energy
Out of sorts: Bad energy