I often feel very sleepy after a hard workout as well. When this happens, I always recall my sister telling me how when she and her husband started running and doing 5k's, they would come home and crash. They now do Marathons, and I'm sure they crash after doing those, but not after doing the 5k's anymore. The stronger your body gets, the more it takes to exhaust you like that.

I also recall many a time coming downstairs in the morning to find my husband crashed on the couch after having gone running or cycling. That doesn't happen very much anymore and he's going stronger than ever.

Always remember to give your body protein after a hard workout. Protein is great for quicker healing of those sore muscles. I'm not a nutrition expert, but you should look into this. I just know my husband hands me a drink of some sort he mixed up after a long ride and says, "Drink this within the next 20 minutes." And I obey! It's a recovery drink of some sort. There are lots out there.