NEW YORK (TheStreet) -- Baird analyst Brian Skorney spent the weekend talking on the phone and trading emails with his institutional investor clients, allaying fears that the biotech sector was going to be decimated on Monday morning.

Late Friday, the Food and Drug Administration issued a safety bulletin warning to doctors about the potential for fatal side effects when Gilead Sciences' (GILD - Get Report) blockbuster hepatitis C drugs Harvoni and Sovaldi are used in patients who are also taking the heart-rhythm drug amiodarone. Most investors first saw the new FDA safety warning for Gilead's top-selling drugs when they woke up on Saturday morning, and they were freaking out.

"People were worried that we'd just experienced the Black Swan event to make the biotech bubble pop," Skorney said.

He calmed investors down on Saturday and Sunday, explaining that the heart drug amiodarone is notorious for causing a lot of side effects on its own and that it's rarely used in the U.S., let alone in hepatitis C patients also taking Gilead's drugs. The commercial impact of this new safety warning would be minimal.

Still, Gilead shares were weak all day Monday, closing down 2%. The major biotech stock indexes were also down about 2% on Monday.

Biotech stocks may or may not be in a bubble, but Skorney hand-holding over the weekend suggests that investors are definitely worried about the industry's mostly sky-high valuations. They're becoming hypersensitive to any event that may force the biotech sector to roll over.

It's a point I made a couple of weeks ago when explaining both sides of the biotech stock bubble debate:

Everyone is looking over their shoulders, worried that someone else will decide valuations are too high and start selling, which will beget more selling. No one wants to be the guy who sells first for fear of missing the next leg up.

To that I'll add: No one wants to be the last guy to sell, either.

Another sign of frayed nerves among biotech investors: The flailing of limbs and gnashing of teeth over the weekend and Monday following Jim Cramer's logical and prudent advice telling investors that it's okay to take profits in the best-performing stocks such as Biogen (BIIB - Get Report) , Regeneron Pharmaceuticals (REGN - Get Report), Celgene (CELG - Get Report) and Gilead.

The biotech bubble watch continues. 

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.