Keep telling yourself you will take a break in 20 minutes….when the 20 minutes is up, say “you know what, I can do another 15 mts. THEN I’m going out….” Do that in short increments of time until you really can’t sit/stand any longer….then refresh yourself quickly and go back in….Your entire year depends on it….
Oh, and find a shul where they sing all the beautiful haunting/joyful tunes…..it literally helps enhance one’s concentration and fervor. Also, try to daven where you feel somewhat connected to the people around you, because we pray in plural after all. Hope at least one of these ideas helps!!
Maybe personalizing the prayers will keep your focus. Try to look at all the prayers before Yom Kippur. Insert tags to remind you of what YOU need to pray for in the places where you feel appropriate. It helps to bring the Tefillos straight to where your own heart needs it.
try going to a Vasikin minyan where i get home by 12:00 then I can sleep until Minchah. another suggestion, bring an english machzor where they have a lot of reading material.