And I was then double surprised that being inside the sun for a nanosecond would be so devastating!
10^-5 J on the surface, when 5 J is needed for a burn
Surface of the sun is a few thousand degrees, inside is a few million
So like a jump off 10^3. No problem, should still be fine.
Not even remotely! I didn't look too close, but the equation he linked has temperature raised to the forth, so a temperature jump of 10^3 would result in 10^12 difference in energy.
Which would increase the 10^-5 J on the surface to 10^7 J. Which explains why you'd only have femtoseconds!