Why am I so tired after swimming?

I just started swimming last October, and have been through different phases with swim tired.

When just starting out, I was often swimming very ineffeciently and burning vast amounts of energy for little forward motion. It was just a whole-body exhaustion. That effect has diminished over time.

As I've become a better (still not good... maybe should say 'less bad?') swimmer, I get a different kind of post-swim dopey thing going on. It is almost like being buzzed - sort of a warm, sleepy feeling from head to toe. I have no idea what the physiology underlying this is. It does seem to be a stronger effect when I swim harder/longer.

This sounds very familiar.  I get the same feeling.  I swim at lunchtime usually and I often have this weird sort of sleepy feeling for the rest of the day.  I almost wonder if it's the chlorine and my sinuses acting up as I often have a running nose for a good solid day after a swim.  Otherwise I can't really explain it.

Normal.  It is because you are truly getting a whole body workout. 

The afterglow of a good, hard swim is the best post-workout feeling ever. 

I do about 24 laps (lengths) in 18 min in a 25m pool.

Normal.  It is because you are truly getting a whole body workout. 

The afterglow of a good, hard swim is the best post-workout feeling ever. 

Welcome to BT and congrats on picking up tri

Yes, swimming is form, form, form first. It's much more like a golf swing or playing the piano at first than an endurance sport, which is why your fitness doesn't cross over. Definitely get together with your swimming friend; I'm sure he (he?) can at least get you started. Swimsmooth.com has some great tips, as does this required reading:

Bigfuzzydoug's Ten Points to Swimming

Another reason, in addition to all the ones stated, is that (in my opinion) the water cools you down a lot and takes a lot of heat out of you ... this makes me feel tired. Could just be my imagination, but it feels that way. All I want to do when I get home is have a hot shower, hot drink, and eat the house down.

Some points to consider -

How warm is your pool?  If you are overheating, it will exhaust you.  Find a cooler pool, ask them to turn it down, don't overdress for the swim.  About 82 is my max for an indoor pool if I want to get a workout in.  Where I swim has done warmer at times for an elderly workout group, but the temp does not go down so easily.  It was a battle to convince them they can't do this if they want to continue having lap swimmers there.  Personally I would prefer 70-75 but I like it chilled...

Stay hydrated.  In a one hour session I lose three pounds of weight - so I am drinking a lot of fluids to stay ahead of this.  As you know from running or biking, it will catch up with you.

Otherwise like others have mentioned, swimming is a whole body workout.  Until you buildup more stamina, you may wish to use a pull buoy so you are using your legs less in the pool.  If you are kicking aggressively, this can tire you out and steal away time from your upper body form and workout.

have fun!

This is a really helpful thread. I thought that I was the only one who got the post swim daze.

I swim at lunch and it effects my performance at work for the rest of the day.

I'm finding with swim that efficiency is a bigger deal than "fitness" as defined by aerobic capacity or body composition. It seems to me (as a beginner mind you) that swimming improvement is coming from practicing and learning technique than from improving fitness.

One other thought - I also have a friend who was a collegiate swimmer. She was the first person I went to for swim advice. What I found is that being a fast swimmer does not = being a good swim teacher. She could see what I was doing wrong but didnt know how to help me correct it. Youtube has helped. I am a Total Immersion technique fan but a lot of people arent. Good luck! I bet with some coaching you take 1min per 100M off that time pretty quickly. 

Great Point!  The average age is very old at the wellness center I train at.  It feels warm and I will check on that next time I workout.  Also I don't drink any water during my swimming session.  Granted I only swim for 20 min right now but bringing a water bottle wouldn't hurt.

Any U tube links that you recommend?

The fatigue is sport-specific. 

I had the exact same experience when I started swimming 'for real' 3 years ago. Was in great shape for running and cycling - could run a HM at 6:30min/mile, finished marathons, and was riding 80-90 mile bike rides every weekend with 5000+ft of climbing. 

Expected to jump in the pool and find 1hr of swimming pretty easy given my slow pace,and my ability to hold a high LT HR on run/bike.

To my amazement, I got completely toasted on the swim - and I wasn't even going hard or fast. Just brisk aero pace swimming at 2:15/100yds, and I was dog tired the rest of the day after 20 minutes. Once I started doing intervals, it got even worse - I was more fatigued from those 30-40 mins in the pool than from a 2 hr hard run. Felt ridiculous. Took 3 months of serious training just to get over that hump.

It's definitely sport-specific. 

Sorry, had a chuckle over the bolded.  How does one overdress for the swim?  I mean other then a wetsuit?  Well, there is that suit TriAya has been wearing...