The S&P 500 fell by as much as 10 points to 1984 today.
The level to watch in the day ahead is 1978, that was the September low. If it breaks it could be an early signal of trouble in the stock market and more broadly.
S&P 500 daily
I think it will take some kind of negative surprise to spark more fears but the inability of the market to rebound following a better China manufacturing PMI is worrisome.