If his meds are going to be effecting him that badly, then you probably need to line up some help with the girls. Being dizzy/feeling sick makes it really hard to watch the kids, and probably 10X that if he's not used to doing stuff with the kids.
Pre-plan some stuff for him/them, too:
Plan out meals and get everything ready for him. IE-make a casserole to pop in the oven, or clip pizza coupons and attach a $20 to it, with the pizza place's phone #.
Put together a couple of boxes of activities --1 box can have 1 new coloring book for each child and some stickers (if you think they'll fight, get them the same ones :). Another box could contain a movie (having them sit & watch a movie might not be the first choice, but having them be out of trouble and letting dad not worry when he's feeling sick makes it probably worth it, imo).
And/or have a relative come and take them to the park/movies/zoo, etc. (Money set aside to pay for admission, if needed).
They will be okay. Make sure the kids, if they are old enough to understand/help, know that Daddy is not feeling good and that they are to be on their best behavior and to help him out as much as possble, and not give him a hard time, because if they do, when you get back, the consequences will be tougher.