Any sign of a possible seizure? This would provided evidence explaining his sudden decreased mentation, H/R-BP a bit difficult to throw in that box thogh.
There is also potential that this patient may be volume depleted and in an early stage of shock. With that, beginning treatment with 02 a line and a fluid challenge seems a prudent initial intervention (provided your respiratory assessment shows no signs of CHF). From there, ya gotta go down the drugs vs Neuro route. Despite his overall lack of apperant "tracks", addicts can be creative about getting there "fix"..this warrants some additional invesigation and prehaps a whiff of naloxone. In my earlier life, we had an entire summer of patients "foilig" Heroin mixed with Cocaine, Many of them presented in a manner very similar to the one you are discribing.
If not that, strong thought needs to be given to the potential neurologic injury that may be present, Again, monitoring, providing fluids and looking for chages VS, This patient could very likely have undiagnosed cardiac issue that has not presented until the day off the call.
In the bus, I'd probably run a 12lead along wth throwing in line etCo2 to gauge the effectivness his ventilatory efforts, If no changes have noted up to this point-I'd probably give him a whiff of Dextrose12.5grams, a milligram of naloxone and re-assess, From the limited information given, I'm assuming his airway is, moderatly patent. If it becomes concerning at any point in the trip---we'll go down that road when we get there.
Out of curiosity, I'd want to know a good deal about the events leading up to this. My gut tells me this is either a
1, Seizure of unk etiology (possiby from piano that fell on his head two days ago)
2. An undiagnosed Cardiovscular injury Or an undisovered vessel malformation that has begun leaking,
3. Ingestion of, or exposure to both illicit and non illicit sustances.
There are literally thousands of working "differentials" for this case given the minimal data provided.
:fish: Just my 2 cents,,,,,looking forward to following up on this.