She read the letter again and broke into a cold sweat.

Why should that cause him to break into a cold sweat?

Nothing to make her break into a cold sweat, on first or even second glance.

"But once it gets over two inches long I break into a cold sweat."

At each stop he would work himself into a sweat while speaking.

By the time they were back in the room, she had broken into a sweat.

You reach a stop sign on a hill and break into a cold sweat.

I'd gone into a cold sweat by the time I reached the pier.

He also got into a sweat with the people at the Soviet embassy.

That means you must work hard enough to raise your heart rate, become short of breath and break into a sweat.