Stress
Deadlines can be a real killer. But while scrambling to turn in on time a report on that new product is its own hassle, the underlying need for the report brings its own pressure, too.
You might be trying to figure out if the new microwave oven emits too much radiation and can cause brain cancer down the road, or if a new blush makes women break out in hives. Maybe you're trying to break down an infant formula that has traces of chemicals that give babies the power of flight (actually, that would be pretty cool, unless you're the unlucky mom that has to try and coax her child down from the ceiling).
Being responsible for spotting these bad qualities, and stopping their production in their tracks, is a big job. You can't miss a single detail, or people might die. Really.
But FDA scientists have to work through the stress and keep a level head. Add to all this the stress of companies lobbying you to approve their products, and you'll want to take two aspirins and take the rest of the year off.
But no pain, no gain. Remember, FDA scientists are protecting lives, one product approval/rejection at a time.