Setting the where aside for a moment, I think the first question is how would your average person go anywhere in that case?
If gravity were to suddenly start pulling everything sideways at 9.8 m/s², then anyone who happened to be outside at the time is probably already dead. They would have "fallen" sideways (or been dragged along the ground, if the pull is sideways and slightly downwards), accelerating until either they reached terminal velocity or until they slammed into the nearest building, tree, or cliff. Basically anyone more than about 20 feet from a vertical surface is likely to sustain serious injuries when the gravitational pull shifts, if they're not killed outright. In either case, those people aren't likely to be going anywhere.
Your most likely survivors will be people who were inside of buildings at the time. And probably only smaller, wider buildings, with a low center of gravity, as skyscrapers probably cannot withstand a 1G horizontal load. So a person inside of a house, for instance, has a decent chance of surviving the transition. So too does the house, if it has a deep/well-anchored foundation. The person inside could move around (inside the house, that is) by walking on the walls. Once they want to go outside, it's another problem entirely.
If gravity is pulling things sideways, then essentially every door in every house/building now opens to a sheer cliff. To go anywhere, a person needs to traverse that cliff. Which for a person of average strength/physical fitness and not in possession of advanced rock-climbing knowledge and equipment is going to be virtually impossible over any nontrivial distance. 947
Maybe a professional climber who happened to survive the initial event unscathed and had their equipment on them at the time would be able to make some progress. However <PERSON> is probably screwed once all the food in the house is gone.
But let's assume you've got someone who survived the gravitational transition and is able to move about (and let's assume that the planet hasn't torn itself apart or otherwise been rendered completely uninhabitable...which is liable to happen from a strictly scientific standpoint but also not really any good for storytelling). Where do they go? I can think of a few options:
* Forests - If you can safely reach a dense forest (and it's still standing; taller trees may well suffer the same fate as skyscrapers), you may be able to use the trees to move around more easily. Moreover, they may provide a source of shelter, and any birds and other small woodland critters that survived may provided a source of food (which is easily accessible, as "climbing" a tree is now as easy as walking horizontally along its trunk). Over time you could potentially construct walkways/bridges and similar structures to make moving around easier and safer.
* Shopping Centers - Think grocery stores, malls, and similar buildings that tend to be large, short, wide, and solidly constructed. These may still be largely intact, would provide a decent-sized surface to move around on, and will contain extensive stores of preserved goods that you're going to need in order to survive. If you can get inside they might provide some decent shelter as well, although the typical layout (large, cavernous interior spaces) might make this quite hazardous. Given sufficient time and resources, however, you could potentially rework all of that interior space in a way that better accommodates sideways gravity.
* Natural Cliffs - Ideally you want to get back into a situation where a large area of solid ground exists in the "downwards" direction. The best option for that sort of thing would be eastward-facing cliffs, and/or mountain ranges (if they're steep enough). Cliffs located near farmland/fertile soil might be ideal, as with a bit of effort you should be able to liberate some of that soil (if the gravitational transition didn't do so on its own) and relocate it to your cliffs. Then you could look at reestablishing basic agriculture, expanding your living area by quarrying the surrounding area, and possibly creating a tunnel network to access nearby locations of interest. 121