Here is an infographic I made for my website One Peso a Day. It shows the timeline of recessions in the United States as well as the generally accepted reasons for why they occurred:
We can see here that the longest span of time without a recession is 10 years. The last recession happened 9 years ago. IF this trend continues, the next recession could occur by the end of 2018. Make sure you have enough stockpiles of liquid assets aka cash and less risky investments.