Strange wobble at work

So yesterday I had a really weird day at work. I started my late shift at 2pm and was feeling ok. An hour or so later I had problems with a label printer it just wasn't working and kept telling me there was an error. After a few attempts I lost my temper and used the phrase I hate to use " it always happens to me". My manager came over and told me there was a problem with it and IT were sorting it.... All this stress could have been avoided if someone had told me. The result of a silly situation was I had to take some diazepam as prn to calm down. As the diazepam kicked in so did the yawns and feeling drowsy.
2 hours later while just chatting to a colleague I got upset from nowhere, I couldn't control the tears and I was on a shop floor with customers around. My colleague was supportive as always and I went on to pull myself together.
I just can't explain what happened and how my mood can change so quickly from ok to angry to stressed to sad. God I hate this illness and trying to carry on working with it is so hard, I'm surprised I haven't been sacked for what must look like bad behaviour.