I'm 18 years old and at a healthy weight (my BMI is 18.5, I come from a petite family). but my resting heart rate is around 112. I'm guessing that's not good?
advice, kids? toss it here.
You should talk to your doctor... over 70 is a high resting heart-rate. If that wasn't a one-off i.e. you hadn't just been exercising or in a stressful situation, then it could be symptomatic of a thyroid problem, infection, a weak heart, anaemia or other problems...
Go to see your doctor straight away.
I think some people can just have fast hearts. My fiance and a girlfriend of mine have fast hearts but their docs said it's no big deal. I understand that people that are very fit have fast hearts. But like GI said, you should still see your doc to be certain.
A heart rate over 100 is not ok and indicates a problem. Barring the absence of a thyroid disorder, in a young person like you I would think of an electrolyte imbalance and dehydration. Are you eating enough? Drinking enough fluids? You should go to the emergency room right away. Do not play with this - when your heart decompensates, it indicates a serious problem. Even if it is a thyroid problem, your heart rate needs to be controlled as does your thyroid. You need medical attention.
Do you take ADD/ADHD medicine, by any chance? That would do it.
But, you do need to see a doctor, your HR is a sign that something is wrong. Do you exercise? Regular cardiovascular exercise lowers the HR - but you should check w/ a doctor before you start an exercise program (it's just going to raise your HR higher, which might not be safe.)
Was this heart rate reading done at your doctor's office? If so, it is possible that you were just nervous, which apparently isn't uncommon when people see the doctor. Maybe try taking your heart rate when you're just sitting around at home and see if it's still high before panicking. Good luck.