The S&P 500 plunged over 3.5% on Thursday (its worst day since June), dragged down by the biggest tech names like Apple, which saw an 8% drop just a few days after its 4-for-1 stock split. And according to some strategists, the selloff is indicating a shift out of the high-flying (and expensive) tech names that have led the rally thus far.

“I think part of this is a little bit of carry over of what we saw yesterday, which is some of that rotation out of some of the stay-at-home trades that have been performing well for some time, and … overall, the tech names [are] weighing down the S&P 500,” Charlie Ripley, senior investment strategist for Allianz Investment Management, tells Fortune.

Part of that rotation may be due to the recent announcement from the Centers for Disease Control and Prevention telling states to prepare to distribute a vaccine by Nov. 1, giving investors a possible glimmer of hope for beaten-down industries (and stocks). “I think that announcement in particular was probably one of the catalysts [for the rotation out of tech], and if you look at the names that have been doing quite well, the tech names, … it’s that rotation out of those tech names and people taking profits and deciding to reallocate,” Ripley suggests.

Indeed, tech titans including Apple, Facebook, Alphabet, and Amazon were all down at least roughly 4% on Thursday. The Dow, meanwhile, plunged over 800 points, while the tech-heavy Nasdaq fell roughly 5%.

But for other strategists, “watching this rotation we’re seeing, we’ve had bouts of this in the past and it’s been fledgling and hasn’t lasted more than a few days,” Liz Ann Sonders, chief investment strategist at Charles Schwab, tells Fortune.

And this shift out of tech could easily lose steam. In fact, according to Sonders, “for this shift toward more classically cyclical areas—financials, materials, industrials—[to last], I think it’s going to require some consistency in the economic data, at least marginal improvement,” she says. “That would be the risk for the rotation trade, is it not being enforced by the economic data.”

That may be a challenge moving forward, as although the data has improved somewhat, the recovery appears to be losing steam. And heading deeper into September, investors may need to prepare for more volatility, as the two months before an election are historically a bit weaker for investors.

A ‘healthy little correction’

Meanwhile, the market’s record-breaking month in August, which saw not only a new high for the S&P 500 but a so-called perfect week for markets, may have put valuations at risk: “With valuations already at all-time highs, the market is looking stretched, and stretched valuations have historically been vulnerable to a snapback,” Brad McMillan, chief investment officer at Commonwealth Financial Network, wrote in a note Wednesday.

Looking at the performance of indices like the heavily tech-focused Nasdaq over the past month, “I think it was time for some rebalancing and taking chips off the table,” notes Ripley. “By and large, it looks kind of like a healthy little correction here.”

Indeed, Randy Frederick, Charles Schwab’s vice president of trading and derivatives, told Fortune last week that the markets had become “irrationally exuberant,” and that the subsequent rise in the VIX, or fear gauge, alongside the markets signaled a “reversal to the downside.”

In fact, last week, Frederick called for a 2% to 4% correction—right around the S&P 500’s 3.5% drop Thursday.

But this pullback certainly doesn’t mean the party is over, say some analysts.

“We don’t believe the bull market is going to end any time soon, but a healthy pullback or even a correction is part of all bull markets,” Chris Zaccarelli, chief investment officer at Independent Advisor Alliance, wrote in a note Thursday. That why he’s encouraging investors to “stay the course” and “ignore the news of market volatility that is a natural part of investing in equities.”