More likely than not, it's because you're slightly dehydrated and because your electrolytes might be off a little. When your dehydrated your pulse increases in response to having less fluid volume in your body. Also keep in mind that it's all relative. As long as you have no other symptoms, you should be ok.
Jess
Edit - I removed your title from your name. We are all peers here and we leave our titles at the door. 
Please remember, we do not dx on HW, we share info and knowledge, caring and avice.
Post Edited By Moderator (stkitt) : 5/10/2011 4:27:32 PM (GMT-6)