Stocks are hot again. But are they too hot?

Record Rally: A gold medal for stock investors
Record Rally: A gold medal for stock investors

It's a tale of two markets.

On the one hand, it's starting to look as if investors have once again drunk the tech Kool-Aid -- just like 1999.

The Nasdaq is at an all-time high. Two recent initial public offerings, text messaging firm Twilio (TWLO) and Japanese social media giant Line (LN), are soaring.

GoPro (GPRO) and Fitbit (FIT) have rebounded sharply from their lows. Facebook (FB) and Amazon (AMZN) continue to surge.

But before you shout "Bubble!" -- take a look at some of the other stocks that are leading the market higher.

A dozen of the 30 stocks in the Dow Jones Industrial Average are up at least 10% so far this year.

And the top gainers in the Dow are stodgy, and dare I say, boring, healthcare and industrial firms. Caterpillar (CAT) is up nearly 25% this year. (That darn CAT!) 3 (MMM)M, Johnson & Johnso (JNJ)n, Merc (MRK)k and UnitedHealt (UNH)h are all up about 20%.

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So the strength in some of these defensive stocks -- which also tend to pay healthy dividends -- may be a sign that investors remain nervous about where the overall market (and economy) is heading. Investors will take gains wherever they can get them.

"Investors are chasing yield. But people also want to put their money into something that's going to grow," said JJ Kinahan, chief market strategist at TD Ameritrade.

To that end, two of the Dow stocks sporting double-digit increases this year are old school tech giants IBM (IBM) and Cisco (CSCO).

Big Blue and Cisco are not Facebook and Google. They are two companies whose best days are probably behind them from a growth standpoint. But their dividends each yield more than 3% ... twice as much as the yield on a 10-Year U.S. Treasury bond.

"Investors have moved away from bonds and want more conservative stocks with high dividend yields. It's a fascinating time," said David Smith, chief investment officer with Rockland Trust.

Walmart (WMT), a retailer that tends to do well when the economy is lukewarm as opposed to overheating, has enjoyed a solid rebound from a year ago, surging nearly 20% too. Part of that may be due to its steady dividend as well. It yields 2.7%.

But Walmart, interestingly enough, may also be helping to fuel the tech rebound. Its purchase of online retailer for $3.3 billion has investors wondering if other so-called unicorns (as well as public tech firms) might also get scooped up.

Related: Why Google, Microsoft and Walmart are gobbling up tech companies

Another hot startup, Dollar Shave Club, just sold to Unilever (UL) for $1 billion as well.

Dan Levine, managing partner at Tenfore Holdings, a venture capital firm in New York, said there may be continued demand (both in the public and private) markets for online retailers.

The success of some e-commerce startups -- not to mention the dominance of Amazon -- is proving that online retail is a legitimate business that will attract investors.

Related: 5 reasons why stocks may keep going higher

Still, Levine isn't sure that there will be a surge in IPOs like there was during the last tech bubble. He notes that the bar to go public is higher now since there are more rules and regulations.

So the only thing that investors may be able to realistically expect is more volatility.

Keep in mind that it was only back in February when stocks were trading at their lowest levels since 2014. CNNMoney's Fear & Greed Index was showing signs of Extreme Fear a few months ago. Now? It's flashing signs of Extreme Greed.

"Equity markets could continue to push for new highs, but we believe they are also susceptible to periods of steep losses," wrote Lara Magnusen, a portfolio manager at Altegris Advisors, in a recent blog post.

In other words, buckle up!

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