My 17 year old foster son is nauseus and vomiting. He is taking over the counter anti nausea meds which don't seem to be helping. He found his tongue was covered in black slime after his last vomit, which he scraped off with a toothbrush. He has no fever. Complains of dizziness. My plan is to let him get through the night, and take him to our family physician in the morning unless things get worse before then.

Does this sound unwise?

Ginger and green tea are great for an upset stomach, cola or ginger ale would also help with the nausea if you have nothing else.The black slime sounds like bile to me, so I'm guessing at this point his stomach is empty.
Without him running a fever, the only danger I can think of would be dehydration. Look at his pupils to see if they are dilated. This might not be an illness, but the side effect of psychedelic drugs.