What to put on self-certify sickness form?

[happypotamus]

I was sent home from work at the start of the shift the other day. Back today, so will have to fill in a form to discuss with my manager. The problem is I have no idea how to explain what was wrong with me in a couple of words. I was exhausted from a mixture of day and night shifts over the previous 4 days and not nearly enough sleep, but you can't be off sick for being too tired. There is also a back story where I have really struggled to cope this year with the stressful, demanding job I have done for over 10 years. I have described the other day as "you know when you are so tired you could cry, and the 13 hour shift seems like an impossibly long time? That. So I did cry because I had no idea how I was going to get through the next 13 hours, and then I couldn't stop crying and it all fell apart and I couldn't go back to pretending to be ok."
Does that make sense to anyone, and does anyone know what I call that on the form? Just lying and saying I felt sick is unfortunately not an option.

Have you been to the doctor since being sent home? Have you ever been diagnosed with anything that would explain your symptoms?

Just summarise the symptoms - fatigue etc

No, I haven't been to the doctors.
I was diagnosed at the start of the year with very low vitamin D, which I had hoped would explain my tiredness and inability to cope, but the treatment didn't solve all my problems.

Exhaustion?

I've put stress and exhaustion on a self certify form in a similar situation and it was accepted without question

Apart from the shift you were sent home from, have you missed a shift? If not, I think I'd put "sent home by X due to exhaustion" or similar.

No, I haven't had any time off sick otherwise for a couple of years when I last had a vomiting bug.
hmwhatsmynameagain that's interesting that you put stress and exhaustion. In my head, exhaustion= tired, which isn't a reason to be off sick (even though I realise that what I felt that day was not just my normal level of tiredness). Stress might be the answer with or without putting exhaustion too. Does putting stress as the reason for sickness automatically trigger a stress risk assessment? I don't want one of those.

My head is very muddled by this, so thanks everyone for helping me work it out.