> Name a single deflationary spiral that has happened.
None whatsoever.
> Identify how much spending you can postpone until next year.
Everything except for life's necessities.
> Reflect if a deflationary spiral is even remotely likely.
It isn't but it's an interesting thought experiment.
A world with a large deflation is probably a world in which all natural resources have been harvested and the only things that still flow freely are sunlight and rain.
The extremely strict monetary policies of German president Hindenburg, a reaction to the hyperinflation of a few years before him, caused a deflationary recession that directly preceded the rise of Hitler.
Japan has had zero net deflation in the last 30 years. Their CPI is higher today than it was in 1990 for example.
Here's what Japan had:
1) Too much monetary expansion in the 1970s and 1980s, leading to bubbles in both real estate and the stock market.
2) When monetary expansion slowed down, they suffered the popping of both of those asset bubbles.
3) In response to that fake boom ending, they turned to accumulating debt.
4) That debt has led to protracted stagnation for ~20 years. Which has now led to currency debasement to devalue that debt, because it's consuming so much of their budget, and the the central government can no longer borrow from Japan's savers (because their savings rate is non-existent now).
You can say they have had net inflation if you pick your time range correctly, but the graph shows spurts of deflation followed by spurts of deparate inflation via QE that doesn't solve the deflation.
Google "Japan deflation" today and you'll get articles from yesterday describing how they are still trying to fight this problem.
Identify how much spending you can postpone until next year.
Reflect if a deflationary spiral is even remotely likely.