Why is Izzie Stevens falling behind at work lately? Who is more immature, Mark or Callie? Will Owen and Alex be able to save a seizing patient with seconds to spare?

These are the questions posed by three all-new previews of tomorrow night's episode of Grey's Anatomy, in which Izzie's health problems are finally faced head-on.

Whatever the specific condition, it's serious. ABC's just-released logline for the March 26 episode says "[Izzie's] condition requires her to undergo a difficult surgery."

Anyway, here's the first of three previews for tomorrow night ...

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Follow the jump for two more Grey's Anatomy sneak previews from "I Will Follow You Into the Dark," and let us know what you think by leaving comments below ...

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Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.