Why is my Betta Fish lying at the bottom of the tank looking dead and not eating regularly?

My Betta does that all the time, don't worry its just maturing, you know how children like to play but as you mature that changes. But, if it not eating, did you change the food based on its regular diet? Maybe you should try more variety, try freeze dried bloodworms, trust me...your fish would go crazy! Also, change the water, sometimes if the water is dirty, then bettas become very inactive, make sure she is getting oxygen, etc.