Well, there is a number of things that could mean. First of all, how old is your gecko? If it's a year old, it may be going through a sort of hibernation. They won't eat hardly at all but their weight stays fairly constant and their tails plump. If this is the case with your leo, then just keep offering it food every day but don't worry if it doesn't take it. As long as it isn't losing weight.
Now, when did you get your leo and from where? Petstores are known for carrying leos that are housing parasites such as coccidia (which my first to leos had and survived through) and this can cause lethargia, anorexia, vomiting, many things but usually the first symptoms are lack of appetite and acting sleepy. They can house the parasites for up to a year without showing any symptoms. This can be fixed by taking a fresh fecal to the vet and getting a medicine such as albon suspension (although there are others better since albon can cause dehydration)
But for now, just watch its weight. If the weight is staying fairly constant and it's still eating a little bit, then it should be ok. You can help it out by placing a small dish of pure calcium powder (NO vitamin D3) inside tank for it to access at all times. That way the lack of calcium through food won't cause MBD.
Any other questions and feel free to email me at leogeckogirl@gmail.com
-Rien