Breaking Back Into It

Hey everyone! I was a competitive swimmer when I was younger, for about 6 years. I have also raced motocross and BMX my entire life, until about a year ago. I had a really bad crash back in 2007 during a BMX race that all in all, left me with an incredible severe concussion, broken eye socket, and a lot of post-crash issues. Added on top of all of my other injuries, I'm a complete mess and decided it's time to get back into the pool. Since I've been an athlete my whole life, being only a little bit out of shape and losing all of my tone that I've had for as long as I can remember absolutely kills me. I can't go to the gym anymore, I can't run, and swimming is my only option for a workout. Don't get me wrong, I'm completely excited to get back in the water! I love to swim, it's in my blood. I just almost feel overwhelmed right now and don't know where to start. I'm being hard on myself because I know that I used to swim a few thousand yards a day, and I'm just not there anymore. I'm not terribly out of shape, only a little bit. I'm back on my old diet, so there's no worries there- it's just the exercise portion. I just was wondering if anyone could tell me a good beginning workout to start out with? Any tips? Thank you so much everyone!:)