Just like the title implied- what causes that bad taste in your mouth after taking a nap or sleeping for a night? and what exactly are you tasting?
In addition, please excuse me for my deluge of initial posts. These are questions I have accumulated over the past year that I haven’t been able to find any decent answers to. Thanks in advance for everyone’s input. 
You know how you’ve been told that people’s mouths are nasty? It’s not really a joke.
I don’t know what species are there, but there are a number of microbial species that live in your mouth. If I understand correctly, you’re tasting the products of the microbial processes going on in your mouth. This is part of why it’s so important to brush your teeth before going to bed (something I will be doing shortly). The brushing gets rid of both food particles and some of the microbes. I doubt (but don’t know) that brushing gets rid of many of the microbes. It’s done to minimize the amount of “food” for them.
The reason you taste it more after sleeping is that your production of saliva goes down. Your saliva produces several enzymes that break down food products, such as amylase (particularly effective against starches) that reduces “food” for your microbial buddies also. It also has a weak anti-bacterial effect on its own. Less saliva means more hospitable conditions for the microbes, and nastier breath for you.
Again, I suspect a dentist or a SDSAB member will probably have a more in depth response for you, but this should scratch the surface of an answer.
Then there’s all that foul language you used in your dreams. 
Actually my experience is that the taste in my mouth is much more pronounced when I’ve brushed within an hour or so of falling asleep.