Energy means a lot in a game, its attitude, focus and multi-tasking. Its harder to multi-task with age, but at least I get that cognitive exercise running a game and pushing back the anxiety feels like diving into frigid waters (you fight the cold with energy and fatigue).
My longest sustained game since I came back was the GURPS Modern Fantasy, adrenaline and panic fueled my emotional energy entertaining players after a long hiatus. I guess emotional energy is the best I can offer. Growing up with RPGs, its easy to channel that enthusiasm in a game and rally all that mental energy. Note that I have to wake up 5am to run a 7am game, it is the best schedule to accomodate a lot of people and still have quality time for the family.
I'm really looking forward to running again in September 7, despite all my other worries regarding game prep at least I don't have to worry about motivation and energy. To my players, they can expect much of the same and of course very dark adult themes.