Hi Toby, the way I understand it, if you are not diabetic (but pre) you don’t have to worry about going low as the effect it has on you is not the same, just like a non diabetic going high for a few hours after eating a great big yummy chocolate cake (sorry got carried away there). Your body deals with it naturally. What might happen is that you save yourself from becoming diabetic by keeping it generally low. If you feel it has gone too low just have a snack of something healthy. What is happening with you is natural and the only bad effect is you could faint but basically it is because you are hungry (5 hours is a long gap). I know I should look at which topic area you are posting in i.e. BSD, Fast800, 5:2 etc. If you are doing the full BSD maybe it is not necessary to be quite so strict and you could do the Mediterranean or the 5:2 just to keep your BG in check.
Pre-diabetes is a warning that you should change your way of eating, it is not a diabetes diagnosis. You are so lucky to have had it flagged before real problems occur. Good luck.