This is incorrect enough as to be dangerous (IMPE, I am not a doctor). They are non-drowsy because they do not cross the blood brain barrier effectively as I understand. Second and third generation antihistamines are fantastic.

This isn't true. H1 antagonists, which is the group of drugs commonly referred to as antihistamines, contains two subgroups of pharmaceuticals. There are the first generation antihistamines, which are generally more popular and earn the reputation of making you drowsy, and the second generation antihistamines. The second generation antihistamines are significantly more selective for the H1 receptors you want to block versus the ones in your brain. Doxylamine is a first generation drug marketed under the brand name Unisom for insomnia, whereas a common second generation antihistamine loratadine commonly includes the phrase "non-drowsy" on the box. It still increases sedation, but at a substantially lower rate than the first generation drugs.