Is 4-5 hours enough sleep for a 16 year old
Next time you see your doctor, tell him if he thinks you need more sleep then he needs to prescribe you something to help you stay asleep. otherwise you are going to be on this same schedule.
On average, teenagers need about 9 hours of sleep. But there's a lot of individual variation in how much sleep people need, and not everyone needs that much. But four to five hours is extremely low, especially for a teenager.
Are you on any medication? If you're taking stimulants for ADHD or narcolepsy, certain antidepressants, or a few other things, insomnia can be a side effect. You might feel awake in the morning, but it's still not healthy, and would generally be a sign that your doctor should adjust your meds.
Are you stressed out? If you're under a lot of pressure at school and with exta-curricular activities, then you might be having trouble sleeping and waking up early due to stress. You might feel alert, but you wouldn't actually be getting enough sleep. If you're relaxed and have a lot of free time then that's probably not it, but if you're always doing things and rarely have time to finish everything, then that could be what's going on. Being that stressed out is definitely unhealthy and does a fair amount of damage to your body.
Do you take naps during the day? If you're only sleeping 4-5 hours at night, but sleeping another 3-4 hours spread out through out the day then you're probably fine. I've heard it's better to sleep all at once at night, but I've also heard the opposite, that it's better to sleep in shorter chunks throughout the day. So if that's what you're doing you're probably fine.