Unfortunately your symptoms are a little vague, (as they are in CO poisoning) and could have been caused by one of a number of reasons.
Had you reported someting a little more concrete, (for example, a dead, pink, co-pilot), we could be a little more certain.
Interestingly you havn't reported a headache, (apparently a feature in 90% of toxic patients), but I guess, if in doubt, get your aged aircraft checked.
Diagnostically, I suspect you need seeing pretty soon after the suspected poisoning. One could mess about with "breath test" machines, but there use in diagnosing poisoning is questionable- good fun with cigarette smokers though!A blood test would probably be required.
More info at
http://gpnotebook.co.uk/simplepage.cfm?ID=832176167
I guess the crux of my advice, is, if in doubt, check the a/c out, it 'aint worth messing with that sh*t
