Copied from a similar question I answered:

The fainting woman trope is often used as a literary tool far more so than a historical reality. It's a very easy way to show the woman as the standard damsel in distress, frail and in need of masculine assistance.

Unfortunately there is a stigma for this today that really isn't true. The modern belief is that corsets, stays, or bodies (depending on how far back you go) were restrictive to the point of not being able to breath properly. I'll agree that if someone who never wore a corset or other supportive device put one on they would feel some discomfort to begin with. However, if properly fitted it should not constrict. Tight lacing was as extreme as 6"+ stilettos today. We laugh at women trying to function that way. It was much the same for women back then. Sure, extreme fashion could be an option, but they literally could not do what they needed to do at work or home. As an everyday woman my garments have to allow me to go about my daily business- and breathing is a part of that.

As someone who personally wears historical garments on a regular basis I can attest to being fully functional in a corset or stays (i.e. pitch a tent, ride a horse, sing opera, muck out a pig pen). In fact, it fixes a medical back issue I have that doesn't allow me to stand or sit for very long. What does sometimes cause "faintness" to occur is when I'm wearing a heavy garment on a hot day or spend too much time in the sun, but most women would be smart enough to dress for the weather and wear a hat.

Another similar question posted here that didn't fall into the "corsets make you faint" trap.