OK, so you have enlisted in the Navy as a Corpsman and now you're looking for answers. That's a good thing. Your approach, however, could use some work. In your intro, you asked for information on what it takes to become a SARC (or something along those lines). I provided that information by doing a simple Google search and clicking on the first link that came up, Wikipedia (all reliability issues aside). Now you're asking another question that you could probably find the answer to yourself. You're also missing something. The PST is comprised of: 500 yard swim, push ups, sit ups, PULL UPS and a 1.5 mile run. Threads like this are usually taken more seriously if you start off by saying something along the lines of: "Hey, I've searched for XYZ which led me to ABC website but they didn't have all the information I was looking for. Could someone please fill in the blank regarding..." That shows us a few things.
1) You're a self starter, not someone who wants to be spoon fed all the answers
2) You've already researched the path that you want to go down and now you just need a bit of information filled in here or there
Did you sign on as an HM and then learn about SARC or did you want to be a SARC and then found out that you have to start life as an HM? Did you look at the pipeline they go through? I almost shit myself just thinking about BRC, SERE, CDQC & SOCM...
Here's the thing, I did my research but I didn't do enough of it when I enlisted. I wanted to drive fast boats and shoot bad guys in the face but now, I'm stuck on a giant, gray, floating (barely) thing: chipping paint, sweeping water, painting rust, needle gunning paint, painting rust, grinding paint, painting rust...oh, and did I mention I'm in an advanced electronics rating who maintains multi-gazillion dollar weapons systems? It sounds like you have done next to no research and you want to be one of the baddest Docs in the military? Learn from my mistakes and do your research and do enough of it...then, do some more. All the questions you have asked here sound like conversations that should have been had with a recruiter before signing up. If the recruiter doesn't have the answers, they should be able to find you someone who does.
As far as your question goes, passing a PST should be something you can do with no issue on your worst day, in your sleep if you want to be a SARC.
Scubadew is an active duty HM looking at the SARC route, maybe he could chime in here with something more helpful.
I genuinely hope all/some of this helps.
Here's a couple of threads you should check out if you haven't already:
http://www.shadowspear.com/vb/threads/whats-your-backup-plan.10342/
http://www.shadowspear.com/vb/threads/sitrep-thread-post-your-progress-here.10497/
I sincerely hope we get to see you post in that second one after you have successfully completed the SARC pipeline.