if the drug makes u very very sleepy, then ur sentence is correct. but it is more fluent if add 了 at the end of it. More Example: 1. 一上英语课， 我就昏昏欲睡. whenever I am taking the English class, I feel sleepy... Here u do not need to add 了，coz it is only to describe a fact that u r not quite interested in EN. (Definitely it is not a good studying attitude,ha ) 2. 今天下午我感到昏昏欲睡，因为我没有睡个午觉。 I felt quite sleepy this afternoon coz I had not taken a nap .

你的句子是对的。但是我们不知道“抗组胺药片”是什么，我们都说“安眠药”。

Trillian, are u learning Chinese? Would u like to add my QQ group 187503051, there are people from italki to communicate in Chinese & English in the group:)