You perceive it as unstable because you're using USD as a unit-of-account. As a thought exercise, if you were using BTC as the unit of account, what you would perceive unstable is the US dollar. And what you would see is that the USD value would be trending down against BTC, especially if you choose a time-frame equal or higher than 4 years.
So yeah mate, nothing to see here, keep holding your cash.
And if I choose a time frame of, say, 25 months or 19 months instead of 4 years, my savings lost more than half their purchasing power, which is far worse than anything QE has done to cash over equivalent time frames (ironically over a timescale which has been exceptionally bad for cash and exceptionally favourable to a notional "safe asset" alternative)
No one ever suggests using some S&P500 ETF shares as money even though it also trends up vs the USD. Just like BTC it's also more volatile than money. Unlike BTC it represents something real though.
The point is that USD isn't for holding. It's for spending. BTC is more like a stock or asset than money. Money isn't supposed to be volatile and it's not supposed to appreciate in value.
No, you would literally have to negotiate prices every single day. The vast majority of currencies have less volatility than Bitcoin. People don't think the dollar is unstable in the euro area.