If I was in your position, I would ask my physician for a referral to a sleep clinic. It may Narcolepsy, Obstructive Sleep Apnea due to enlarge tonsils. This is why it will be helpful to get a sleep study done so it can be more accurate to what it may be going on.
You need to see a physician Sleep Specialist.
1.You could have sleep apnea and would be ''cured'' by using a CPAP machine when you sleep.
2.You could have a form of narcolepsy which could also
be diagnosed by a Sleep Specialist.
3. You could have another type of a rare daytime sleepiness disorder named IH (Idiopathic Hypersomnia) which usually appears in your age group and older.
2 and 3 require an overnight sleep study and then what is named a sleep latency study in which you stay the entire next day as well.
I have major experience in living with the above mentioned.
Thyroid: If you are normal weight and exercise with no other systemic symptoms, a low thyroid is unlikely.
I major experience is this issue as well.
Either make an appointment with a highly recommended Sleep Specialist (usually are neurologists or internists who enter this specialty) in your area or have your PC refer you to one. Please...do not put this off. I lost years of quality of life because of the delay in the diagnosis.
I would suggest that you should go to the doctor for further investigation. It might be nothing cos you re away of your normal college sleeping patterns. But it could be thyroid related or narcolepsy. Cant say a lot here, go to the doctor.