Balrogs and Elvish Spirits

[Rumil]

I've wondered if the Balrog had gone into some sort of hibernation in the long years between the end of the First Age and the dwarves' delving.

At first (few years/centuries?) it would have feared discovery by the Maiar, Vanyar et al, but effectively it appears to have slept on until discovered. Perhaps being woken up made it extra-grouchy!