I attribute the drowsiness to the antihistamine and the restlessness to the phenylephrine. I feel it's a bad combination for me.
You can talk it over with a pharmacist or physician about recommendations. I ended up deciding to avoid phenylephrine in the evenings and at night.
On a side note. Before you decide to buy the bottle of extra strength cold medicines, compare the ingredients to standard variety. Most of the time they are EXACTLY the same.