Past performance does not guarantee future resultsThat period is the best example of "this is no big deal".
At the worst, I was down 60% in my 401k; ended the year ~40% down. With dollar cost averaging (I was still working and contributing 6%) my investment graph ($) was back on trajectory in about 1.5 years as if it never went bad.
These are small blips in life if you don't get emotional.