If you have a difficult time staying awake and alert during the day, you may be experiencing excessive daytime sleepiness. Dr. Virend Somers, a Mayo Clinic cardiologist with a focus on sleep medicine, explains the difference between being tired and being sleepy and how excessive daytime sleepiness can have a negative effect on the heart.

Needing to rest your body after a great workout or after a long day of work are examples of being tired—which is different than being sleepy.

“Being excessively sleepy during the daytime is, in a sense, falling asleep very quickly, having a very short period between the time you lay down or the time you sit down and actually falling asleep, and having no clear, obvious cause for being sleepy, or a cause related to a sleep disorder,” says Dr. Somers.

While there are many causes, the bottom line is excessive daytime sleepiness means you’re not getting enough quality restorative sleep.

Using an alarm clock?

“When you need an alarm clock to wake you up, then by definition, you haven’t had enough sleep,” says Dr. Somers. “Because you could have slept more.”

Not getting the sleep your body needs can pose health risks.

“There seems to be an association between being sleepy and having a higher risk of cardiovascular disease,” says Dr. Somers. “We’ve found—independent of other things that we can identify that increased cardiovascular risk—that daytime sleepiness seems to be linked to a higher risk of heart disease, of sudden death, of cardiovascular death.”