sounds more like a PSYCOTIC depressive episode- don't think ketermine would be the drug of choice but maybe some haldol might provide some clearer thoughts.
I am also a psych nurse practitioner.
Yes there seems to be many psychotic features in the mix. As a nurse you would spot the nihilistic delusional nature of some of it. If you have any thoughts or tips please feel free to mail me.
For a more complete description see:
http://www.freerepublic.com/focus/f-chat/1597364/posts
I am currently going through CBT and it is helping.
How I have managed to function these last 5 years I don't know (Thanks to the Lord and my good wife who have stood by me).