Welcome to healthcare Magic!
You should take meclizine
at the most symptomatic hour but be aware it can cause drowsiness
and a fall.
Do not drive four 4hours after taking this medicine, drive to destination first and then take it if necessary.
Meclizine should be started at half the normal dose at your age and then should be built up if needed.
You should get your BP checked, Niacin can cause a fall in BP and can cause all this.
Wish you a great health!