I agree. This is why I stated our 24 hrs limit for taking Benadryl
before flying.
Here are the FAA guidelines from this website
http://www.aviationmedicine.com/allergies.htm

Over-the Counter Antihistamines

"The over-the-counter products such as chlorpheneramine (Clortrimaton,
CTM) and diphenhydramine (Benadryl) found in many commercial products
cause drowsiness. They are not permitted by the FAA and a pilot should
wait at least twice as long as the dosing recommendation after the last
dose to fly. For example, if the directions read take every six hours",
the pilot should wait at least twelve hours after the last dose before
considering flying. These medications may have subtle adverse effects
for much longer in some individuals. Chronic treatment with over the
counter antihistamines requires a 24 hour wait after the last dose
before flying, according to the FAA Guide for Aviation Medical
Examiners."

Decongestants

"Decongestants, such as Sudafed, are often used with allergies to
constrict blood vessels in the nose and relieve the running nose.
Pseudoephedrine, found in Sudafed, and phenylpropanolamine, found in
many other products, are both approved. These medications act
throughout the entire body by constricting blood vessels. Side effects
may include an increased heart rate, elevated blood pressure and
difficulty urinating in men with prostate problems. Because the
frequently keep individuals awake, they are often combined with
non-approved antihistamines sold over the counter. These combinations
of decongestants and OTC antihistamines are not approved within twelve
hours of flying."