For some insight: Sinus tachycardia occurs in response to exercise, exertion, excitement, pain, fever, excessive thyroid hormone, low blood oxygen (hypoxia), stimulant drugs (such as caffeine and amphetamines), etc. Did you have an EKG test? All of the above possible causes would have to be ruled out before there can be a serious heart problem diagnosis.
The probability is high that there is no serious medical problem.