What can cause a heartrate to zoom to over 225 bpm? I went to the hospital but they released me, without running tests, because I am uninsured.

Many things. I'm sorry you had this experience. Your heart rate can go that fast if you have been really pushing exercise, and you are young. If you are middle aged or older, it could be atrial fibrillation, which can be serious. Rarely anxiety can cause the heart to beat that fast, in a normal pattern. High thyroid function can increase the heart rate too. Please get some follow up.
See a doc. Different arrhythmias ca do this and some can be dangerous, please find a local md. Some can be very easily and cheaply treated.