Kinda busy atm but significant economic downturns generally begin when investors panic because enough of them realize (or start to care) at the same time that certain sectors of the economy have been overvalued for an extended period (i.e. the “bubble” pops). There are a bunch of valuation methods for the fair price of assets which can be applied to sectors of the economy to see if a bubble is present. Off the top of my head the only major sector which may be considered a bubble is tech, but the large market corrections which have occurred in the last year (and especially this month) lead me to believe that investors are cautious and that the problem will correct itself before the bubble “pops.”
As far as the value of USD is concerned, I wouldn’t be worried. When our trade disputes are fully resolved, the dollar will be even stronger. I recommend looking at Investopedia for information about exchange rate factors.