Mortgage, consumer, CRE, corporate, and pretty much all other debt levels are at record highs. All major banks are more highly leveraged than they were in 2008. CRE is already seeing elevated delinquency & defaults and it'll likely bleed over to residential RE in the near to mid term. We've also reached the end of a 40 year secular decline in interest rates, the Fed is out of ways to ZIRP the rates again unless it wants to go with the full zombie Japan model where it buys every asset on the market and becomes the first, last, and only buyer. If it tries that the USD just might lose its reserve status and then you're really fucked.
Then you have healthcare & banking making up ~40% of your economy. Both sectors are parasitic in that they impose large costs on all other sectors of the economy which takes away from their competitiveness. Both are required to have a modern economy, but every dollar which a bank or hospital takes in as revenue is a dollar which comes out of the actual wealth producing sectors of the economy.
If you want a far more in depth yet easy to understand explanation of things, I'll refer you to the following book. Mr. Denninger wrote a book on it so that I don't have to.