Fortunately, I think I do, but that is only because the reason why I am so down is due to things that are going on about my life right now.
I have however, also been in the same place where I think you are now too.
There have been times, where I will just feel really down and so low, that I do not want to do anything - and have no reason for it (or so I believe).
Trying to explain that I feel like shit and not knowing why , is hard, and I also think that the person you are telling, also has to be able to accept that.
After some self reflection, any perhaps when you a mulling over, why you feel so down, you might be able to come back to yourself with an answer, and sometimes you don't.
I don't know if I am making sense here, but I am sure, when you know, it will be much easier to explain - until then, I think people including your OH will just have to be patient, providing they understand depression, I truly believe that your OH will be able to respect that. x