Child Has Coughing, Nausea, Temperature Change. History Of Mono. What Is It?

hi my 18 year old son woke up this morning and went to use the bathroom as normal and i heard him coughing and asked him whats going on and he said he felt like he was going to throw up and felt his body temperature change to where he felt very sick and i heard a crash in the bathroom he said he turned around and just fell and grabbed the counter in the bathroom to hold him up from hitting the floor and he went back to his room without knowing how he got back in there but knew to get to his bed. He was very tired when he woke up and he has this happen to him this morning and his temperature is in the 96.5 to 97.0 range right now and he has tested positive for mono in the last month. Can you tell me what he might of had and should i take him in to see his doctor.