You know those moments! You are too upset about something to do anything useful with your time except mooch about on facebook or similar. Usually the last thing that you have on your mind would be to play guitar however, that is where you are wrong.
Emotionally stressful times are perfect for your creative side. You are more aware of what makes an emotional song when you are in this state. I remember a time when I have been upset and was just messing around on my guitar and I suddenly stumpled upon the perfect chord sequence which just made my eyes well up with tears. It is the same with constructing scale runs as well.
In times of emotion, as well as guitar playing, try practicing your lyrical skills. Usually the best way to do this is to just write whatever comes into your head onto a piece of paper. Forget about rhyming words! Rhyming is great for songs meant to be catchy however, if you want words that will connect emotionally with the listener, then write something from the heart, something human that everyone can relate to.
Sometimes, the simpler lyrics are the most effective, so dont worry about writing lyrics that you dont think sound 'professional'.
I hope these thoughts will help improve your playing and writing.