What's keeping Sundar Pichai, Tim Cook, and Mark Zuckerberg up at night

Apple, Facebook, and Google are three of the most powerful tech companies in the world.

But none of them got there by resting on their laurels.

At Business Insider's IGNITION conference this week, we brought together three experts: Piper Jaffray's Gene Munster to talk about Apple, RBC Capital's Mark Mahaney to expound on Facebook, and Marketing Land's Danny Sullivan to explain what's going on with Google.

Moderator Brian Morrissey asked the group what scenario or risks likely keep the CEOs of the three companies up every night.

Here's the quick-n-dirty:

• Apple's Tim Cook cautiously prepares for the onslaught of virtual reality
• Facebook's Mark Zuckerberg frets about privacy legislation
• Google's Sundar Pichai looks warily at the EU antitrust decisions

Apple: VR paranoia

Munster thinks that Tim Cook is likely on edge about the impending shift towards virtual or "mixed" reality. Major tech companies like Facebook, Samsung, Sony, and HTC have all released - or are planning to release - virtual reality headsets, but Apple hasn't announced any new hardware plans (despite hiring a number of augmented and virtual reality experts recently).

"We think mixed reality is a new computing paradigm - the equivalent would be talking about smartphones in 2000, and who knew what an impact that would have," Munster said.

"I think that if you're Tim Cook, you're thinking, 'If there is this shift to more wearables and essentially something that replaces the iPhone, that's going to be a big opportunity for competitors to step in.' And I think it's going to start slow, but ten years from now, I think the iPhone is going to be a much smaller part of Apple's overall business. And I think navigating that is probably the most stressful thing that [Cook] has to deal with."

Facebook: privacy laws

Mark Zuckerberg, on the other hand, has Facebook's virtual reality plan on lock, as it preps to release its long-awaited Oculus headset in Q1 2016.

Mahaney postulates that - besides his new baby - Zuck likely worries about privacy legislation. For example, the company is currently planning to appeal a data privacy ruling in Belgium trying to stop it from collecting information about people that are not its users.

"There's some legislative privacy risk associated with these massive platforms that know so much about us," Mahaney says."That could be a systemic risk for Facebook. If there was something that undermined people's trust in it, some sort of event... Maybe that's [Achille's heel]."

Google: antitrust

Similarly, Google's Sundar Pichai likely has his biggest headache coming from anti-trust issues in Europe, according to Sullivan.

"Their biggest challenge really is on the legal front. The anti-trust efforts are still going through in the EU," he says. "I think you're going to continue to see them get hammered on that in the EU. It could potentially cause them to have to make some substantial changes."

Right now, the European Commission is still deciding whether to fine Google or settle with the search giant, in a case about whether it abused its power and promoted its shopping service over its rivals.

Although the FTC in the United States probably won't go after Google Search again (after fining the company in 2013), it may also eventually take on a new case around the company's smartphone operating system, Android.

"Both here in and in the EU, you could see the de-coupling of Android happen, where it will be 'You can't just wire in Google Search as the default,'" Sullivan says.

And Google could face a challenge from Apple, if the company ever decided to completely get rid of Google in favor of Bing in its Spotlight search product, and make it available as the default search in Safari.

"That has a chance of taking some share away from Google," he says.

Finally, although Google is seemingly working on a new mixed reality product following the failed Google Glass, the company also could be left behind.