One way I get ideas is I like to think of a small mechanic I want to learn and try to fit a game around that.
Like if I was learning to make enemies shoot and follow the player I could make a action gun game, or if I wanted to learn a level up RPG system I could make a very basic RPG game focusing mainly the leveling up system.
ohh sorry I misunderstood. Well it could be anything that starts calm then something big and powerful happens. Maybe a game where the player has to prepare in the first part of the game before something big happens in the second half. I immediately think of preparing defenses for an incoming invasion of somekind, zombies, aliens or even just human war.
Think of games you've played where its chill and you can use that for a calm aspect and then think of ones that have been exciting, stressful and urgent for the second half.
I am pretty sure you can interpret the theme how you like for the jam so you need to narrow that down for yourself as too much choice causes problems, atleast for me anyway! I haven't got any solid ideas right now myself but hope this helps you think about it!
