As/whenever, etc. the fancy takes you
Definition 1 of 1
Pro Tip 1/3Spontaneity
This phrase suggests an action taken on a whim without planning. 
I bought those shoes just as the fancy took me.
Pro Tip 2/3Frequency
Implies no time restriction, action can happen often or rarely. 
He visits his hometown whenever the fancy takes him.
Pro Tip 3/3Informal
Best used in casual conversations rather than formal or academic writing. 
Call me up to hang out as the fancy takes you.