Hi - My 26 Year Old Son Was Home For

Hi - my 26 year old son was home for the Holidays and is now in Lak Tahoe with friends before heading back to San Luis Obispo where he recently graduated from Cal Poly. He has been experiencing sporadic spells of feeling faint and light headed along with an inability to think clearly (very unusual for him). He was driving to Lake Tahoe and found that he could not even concentrate on driving so he stopped in a small town where an EMT checked him over and had him admitted to a local hospital overnight. His vitals and blood tests checked out ok so they discharged him but he barely was able to drive himself to Lake Tahoe. He is very fatigued so I thought possibly mono but he is thinking possibly Lyme disease or an actual brain issue. Any thoughts on what should be checked as soon as he manages to get back to San Luis Obispo (with the help of friends)?