What is autistic inertia?

I keep seeing posts here about autistic inertia. I have to ask what is that?

From the description it sounds like it may be what I am going through at the moment. Only trouble is I have an awful lot of stuff I actually HAVE to do and I don't know how I'm going to find the "energy" for want of a better word to do it.
Any explanations or tips would be very appreciated