If the only symptom is sleeping 10 hours, then I wouldn't be too worried. I would keep an eye on it, obviously, because as a mother your instinct guides you more than a doctor can, in my opinion.
Babies each have their own cycle of sleeping, growth and needs. These change intermittantly throughout life. Sometimes baby may sleep throughout the night and need a couple naps during the day. Then baby will go through another phase of not wanting that many naps during the day and waking up once or twice during the night. Then baby will go back to sleeping through the night and taking one nap a day.
I have two boys and they come and go. They are 4 and 5 years old now. They both sleep really well through the night, wake up some, but pretty much fall right back to sleep (after occassionally crawling in bed with me...lol). I think around 1 year old they stopped taking two naps during the day and would wake up every once in a while during the night. I tried to give them heavier meals at night with more protein and veggies to tide them over. They used to take two naps during the day, about an hour long, until about age 3. Then they only took one long nap during the day, of about 2 hours, until they were 4-ish. My 5 year old doesn't usually take a long nap, but he doesn't lay his head down and maybe fall out for about 30-45min late morning or early afternoon.
I think each child's sleep patterns are different. So, I wouldn't let a friend or relative convince you there is a problem if you feel okay about everything. My one child is a night owl like me, and the other one likes to go to bed early and get up early.
Below are some links that might help. Please know that these are generalities, and every child doesn't necessarily sleep as much as they say.
** SLEEP: AN IMPORTANT PART OF HEALTHY DEVELOPMENT
http://www.childcareaware.org/en/subscriptions/dailyparen...
** UNDERSTANDING CHILDREN'S SLEEP HABITS
http://www.sleepforkids.org/html/habits.html
** CHANGING YOUR BABY'S SLEEP PATTERN
http://raisingchildren.net.au/articles/changing_your_baby...