Why do I only experience vertigo like feeling only when walking in a store but when I walk around outside I'm fine?

Start with doctor. To rule out medical causes for vertigo, see your pcp for exam. If all points to anxiety, get referral to a mental health professional for assessment/guidance. Meantime go to store during off-hours to minimize crowds, noise which may be triggers. Or go to a smaller store eg, neighborhood deli instead of a super center grocery to cut stimulation. Log how you feel and any other symptoms. Best wishes.