How long does the next day groggy feeling last after taking hydroxyzine before bed?

Hydroxyzine is an antihistamine with sedative effects. If you've just started taking it this side effect may resolve in a matter of days to a week or so as your system adjusts to the drug.
If this has been going on for a while let your health care provider know and get their advice. It may be that a temporary lower dose may be helpful or it may just be a matter of waiting it out.
Best regards,
Wildcat

Hello,
I myself had taken hydroxyzine before bedtime for at least a month, because I had trouble sleeping due to high anxiety. I took 50 mg before bed and within 45 mins, I was asleep. But the only downside is that, I felt drowsy during the daytime for weeks. So I had to get off. This is just my experience. Give the medication a shot. Everyone reacts differently. Like Wildcat said; side effects usually resolve within a few days or weeks. But if these side effects go on for a while. Then Let your doctor know.

Tyrese