Go to the doctor! This could be caused by anything and it's better for you that they run tests and figure out the source of the problem.
I was having trouble with this for a while too and there are so many different things that it could be, many of which can be treated really quickly and easily.
On a side note, when I was feeling REALLY sleepy all the time and kept falling asleep at the wheel and at work, someone suggested taking medication for narcolepsy and it helped more than anything. Also, avoiding processed foods and doing cardio a couple times a week gives me more energy than coffee ... It's not so awful if you find a fun class and get into the habit of it.
If a regular doctor can't find anything, find a great naturopathic doctor. I spent six months sleeping eighteen hours a day, saw hoards of different doctors and nobody could figure it why. My doctor recommended a naturopathic doctor. After a two hour interview / exam, she gave me a list of supplements to pick up from a place like Whole Foods and I immediately got better.
Really, get help! At least, you'll get some answers and can stop worrying. Stay hopeful! I'm sure you'll find something ... 16 years is a LONG time.
Hello and hope you are doing well.
Your symptoms of excessive sleepiness could be due to a sleep disorder called Narcolepsy. This sleep disorder is characterized by excessive day time sleepiness, sleep paralysis, cataplexy where the person has episodes of loss of muscle function while awake, hypnogogic hallucinations and automatic behavior.
Narcolepsy is diagnosed by the sleep onset REM episodes (SOREMs), wherein the person goes into the dream phase or REM cycle soon after sleep onset. This is evident in the Multiple Sleep Latency Test (MSLT). It can however be regulated with medications.
You will need to consult your primary care physician, who may schedule you for a polysomnogram (sleep test) to rule out sleep disorders and initiate appropriate therapy.
Hope this helped and do keep us posted.