Tell them the truth - I was in a similar situation this time last year..I bottled up a very stressful incident, once it was all over i let my guard down and it all got to me, I ended up having 4 months off.
(due to difficulties in another office, I couldn't update the risk assessment on a low risk client, whilst I was away he transferred out of our area and into another, on my return from leave I noticed he was back in my area with 3 days left to run on his licence (making him my responsibility again!) once again the transferring area had not released the risk assessment to my area and it could not be updated.......7 days after his licence ended he murdered someone........I was held accountable for the reason that I hadn't completed the risk assessment!!!!!)
Due to the pressure I put myself under I ended up with CFS (chronic fatigue syndrome) I wouldn't wish this on you Karen.