While its painful to see the account drop in value, look at it from the perspective that each time your buying into your investments now, it will be at lower prices. You'll be buying more shares at lower prices and that's going to be better in the long term.
If your time horizon is really that long, this should be a minor blip on the radar. Its painful but since your not counting on these dollars in the short term, it's much better. Someone who is retired or nearing retirement is much worse off.
Ideally, you want to buy as many shares as possible and have the investment skyrocket right before you sell or retire etc. Doesn't happen that way usually though....