I have an unusually fast heart rate for unusually long periods of time. what is wrong with me?

Not sure: That depends on how fast the heart rate is and exactly what the rhythm is as determined by an ekg. There may be nothing wrong with you. Maybe your thyroid is overactive. There are just a lot of possibilities so you need evaluation by a physician.

Tachycardia: tachycardia can be multifactorial. It can be from environmental things such as heat it can be from things to ingest coffee other stimulants. It can be a thyroid problem. There can be a normal electrolyte problem. You can have troubles with your electrical pathways. Difficult to say on line. I would suggest that she to talk to your doctor spa be started with an EKG and perhaps have a Holter

Many possibilities: What do you mean by "unusually fast hr"? Causes of sinus (normal) tachycardia include:fever, pain, anxiety, fatigue, exercise, dehydration, caffeine, asthma inhalers, many other medicines and drugs, hemorrhage, anemia, excess thyroid hormone; then there are abnormal rhythms such as atrial fibrillation or flutter, pat/svt, wpw, and VT - there are many other possibilities. You need an ekg!