Complex sentence: However, the rate of inflation should not decrease until it's negative, which is deflation, which is an overall decrease in prices, since deflation is always regarded as a negative state of the economy no matter how high it is.
Split into simpler sentences: However, the rate of inflation should not decrease to the point were it is negative, which is deflation, an overall decrease in prices. This is because deflation is always regarded as a negative state of the economy no matter how high it is.