High heels force you to push the hips forward when standing/walking, so it changes the posture to something 'more attractive', hence they feel sexy.
Only way I've found to get used to wearing heels, is to just wear them each day, a bit longer each time, start out for half an hour on day one and then an hour on day two, 1.5 hours on day 3 and so on until you're comfy with the time period you want to be out and about in high heels.
5'11" here, so for the most part I wear flat shoes, just because when I'm around the house I'm mostly barefoot anyway, and for walking around town, flat shoes are much more comfortable.
Why do shoes feel different when you get them home after buying them? mostly it's because of the time of day you buy them, for all women (and men too I would assume), your feet will swell up slightly (not necessarily noticeably) during the day, and this can affect how comfortably your new shoes will fit if you buy them in the am and then don't try them on again until the evening after a day out and about. (sorry for that knowledge, big wide feet tends to make shopping for shoes a pain, and you learn the little tricks
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