"dropped to normal" is correct and can be used in written English.
You can use it when you are talking about a change in a value that has gone back to a typical or usual level. For example, "The temperature dropped to normal after the heatwave ended."
His high blood pressure dropped to normal — cured by the now-normal levels of growth hormone.
As soon as the tumor was destroyed with radiotherapy, Mr. Holland's headaches disappeared and his growth hormone levels dropped to normal.
Outside of the Northeast, reports of people with flu symptoms who visited doctors and hospitals dropped to normal levels for late May, said Dr. Anne Schuchat, director of immunization and respiratory disease for the Centers for Disease Control and Prevention.
In these patients, lactate levels dropped to normal in 52% of the patients at 24 h.
The number of adenosine receptors dropped to normal levels, without apparent side effects, and asthma attacks were completely prevented for 12 hours.
My elevated blood pressure and resting heart rate dropped to normal, and later athletic, levels; I discovered passions for hiking steep trails and lifting heavy weights.
If the driver selects a high setting and forgets, the system automatically drops to normal at highway speed.
A spokesman for the Met Office said that by the weekend temperatures were likely to drop to normal for the time of year.
If polymyalgia rheumatica is the correct diagnosis, symptoms will resolve almost immediately, and the ESR will gradually drop to normal values.
A spokesman for the Met Office said that by the weekend temperatures were likely to drop to normal for the time of year, bringing a risk of frost, fog and even wintry showers in some parts next week.
But hearing chair Jesse Jackson Jr. (D IL) noted the obvious: The 2-year bolus of money could prove to be "a double-edged sword" if scientists can't keep going when NIH's budget drops to normal levels in 2011.
