You need to provide more information: 1) Is this in the 'mail app' of the iPad?; 2) Is this a new occurrence?; 3) If you have multiple accounts(s), is this happening w/ one or several?; 4) Have you had problems w/ your 'wireless' connection(s)? - other questions could be asked but these will be a start.
Now if your email was saved as a draft and you can re-enter the home screen, go to the multi-taskbar (i.e. double tap the home button), then press and hold the mail app until the icon jiggles - hit the minus button to 'force close' the program; return to the home screen and try again.
If the 'force close' is ineffective then 'Restart' and if no useful 'Reset' the iPad - directions HERE - if none of these maneuvers are useful, please post back and good luck!