There are not reported fatalities from ingesting psilocybin. Massive doses of LSD may be fatal but as far as I know none have been confirmed. So I can say confidently that you're not going to die as the result of the direct pharmacological action of psilocybin or LSD, if you do your name will go down in medical history.

Both psilocybin and LSD are indoles that act on the 5-HT (serotonin) receptor system. When I was in elementary school I remember this anti-drug bitch telling the class that acid stays in your body forever. Truth is it doesn't, your body doesn't store any of it for any amount of time. It is metabolized and excreted from the body very quickly, well before the trip is even over.