This question may be more about German reference work conventions than about the turn of phrase in the title. (In which case, let the title refer to my current state of mind.)
I found this definition for the turn of phrase in this post's title:
neben der Kappe sein (ugs.): einen schlechten Tag haben, geistig und körperlich nicht gewohnt leistungsfähig sein
I understand what the two parts (separated by the comma) of the definition say, but I cannot make sense of the whole. Usually, I would have expected the second part to be either a qualification of the first, or possibly a paraphrase of it. Here it seems that it's an entirely second meaning, but it is disconcerting that two different meanings are separated by a mere comma. Am I missing something?
FWIW, the two meanings I see are
- have a bad day
- be mentally and physically unaccustomed to performance (or efficiency)