Yes, stocks do go down sometimes.

After the sugar high of 2016 and 2017 — that saw the S&P 500 gain 9.5 percent and 19.4 percent, respectively — Wall Streeters tasted more bitter than sweet in 2018 amid historic volatility.

The Dow Jones industrial average shed 5.6 percent during the roller-coaster year, which saw it test the 27,000-point threshold, at 26,951.81, on Oct. 3 before plunging 3,624.35 points at year-end.

It was a common occurrence to see the blue chip index swing several hundred points in either direction, with it plunging 1,597 points in intraday trades on Feb. 5 before recouping losses.

For the last day of the year, the Dow eked out a gain of 265.06 points, or 1.15 percent.

Elsewhere, the S&P 500 index was off 6.2 percent for the year while the tech-weighted Nasdaq gave up 3.9 percent as once high-flying names such as Facebook and Apple lost their luster.

It was the worst year for stocks since 2008 — busting analysts’ expectations that President Trump’s tax plan would goose corporate earnings and lift stocks.

While the tax plan initially sent stocks soaring, momentum eased on investor worry that full employment and rising inflation would force the Federal Reserve to aggressively hike interest rates in order to prevent the economy from overheating.

Also adding fuel to the fire was the US trade war with China, which stoked fear among the chief executives of global companies.

As for 2019 — once burned, Wall Street is viewing its approach with a cautiously optimistic eye.

“In 2019, we expect modest US market returns and volatility to remain elevated,” said Mona Mahajan, US investment strategist at Allianz Global Investors.

“Markets will likely struggle during the first half of the year as fundamentals, like global growth and liquidity, sort themselves out. Equities should find their footing sometime by midyear,” said Jack Ablin of Cresset Wealth Advisors.

The US and China agreed to hold off on more tariffs until March 1, and observers are hoping a recent Trump tweet on Saturday announcing “big progress” will bear fruit.

Meanwhile, the Fed factor looms, with Chairman Jerome Powell hinting last month the agency plans two rate hikes this year.

But many analysts see hope — provided the economy stays sound. “I think the market is underestimating the chances of a 2019 rally … We could see a nice bounce from where we are,” Michael Antonelli, managing director at RW Baird, told The Post.