My heartbeats have been getting to >100bpms-was about to faint twice. ecg showed sinus tachy. got high fever for 24 hrs once. is it serious?

Caution: It is normal to experience sinus tachycardia with high fever. You need to find out the reason for the fever, and treat the cause.

Many causes: Sinus tachycardia can be a response to many things, ranging from infection to exercise to dehydration among a lot of other causes. If this is recurring, see your physician, who should be able to help you find the cause and the solution to this problem.