FH1101 - re energy & SASless - re calm.
There's lots of energy in a rotor, but not too much.
The kinetic energy of a rotor in a small helicopter is in MJ.
Generally (in J) ~ 0.005 x rotor mass (in kg) x disk area (in m-squared) x rpm-squared; for Glasgow, 200kg, 75m^2 and 200rpm gives ~3MJ.
However, it's powered by a MW or so, so if you turn off the engines from a high power setting and do nothing else, the energy stored is only matched to a few seconds of power.
Other relevant quantities are the energy from forward speed
(in J) ~ 2 x total-mass (in kg) x speed-squared (in kts); for Glasgow, 2500kg and 100kts gives ~5MJ.
And potential energy from height
(in J) ~ 3 x total-mass (in kg) x height (in feet); for Glasgow, 2500kg and 700ft gives ~5MJ.
Each of these energies is comparable, and so all need to be taken into account.
When cruising along, there's a good fraction of a MW going into beating the air too.
While I'm sure you should "Keep Calm", sometimes you'll need to "Act Quickly" as well.