Make sure you mention the woman from your intro into your conclusion. Your essay should come full circle. Also I would work on making your introduction a little stronger. It needs a hook. Something that makes the reader think "I gotta keep reading!" Go into more detail about the experience with the woman having a heart attack. Why was THIS experience so important to you? How does it play into your desire to become a PA? Obviously this experience is very important to you (you're choosing to write about this experience compared to many others I'm sure you've had) so make the reader feel that. And then tie all that into your conclusion at the end.
Remember that your essay has to stand out! But also remember that it's a draft. Your draft is going to be day and night compared to your final result.
Also a tip, if you get stressed with your essay, take a break for a few days (or a week in my case) and then come back to it. Coming back with fresh eyes will make all the difference!