Hey slumber. So what i hear is, you had two different sets of experiences that might be affecting the current situation. One is a series of bad medical experiences, the other is a few bad sleepovers. Its easy to see how the bad medical experiences would affect your trust in doctors now. But the sleepovers probably would have affected your ability to trust your family, when you were very very young.
As you say, and i agree, the event itself was relatively trivial (as were my own), but the awareness of the loss of trust is huge. The extent, and at that age? Not trivial.