Hi Anne and welcome
I'm not surprised at your father being tired and feeling unwell with levels of 30 I'm like that if I reach 19.
I can only assume that your father is either not on a diet or following a hi carb diet from the doctors surgery for levels like that. It might be an idea to lower his carb intake considerablyv that should get his levels down. get him to cut out bread, potatoes, pasta, rice - look at the advice in the low carb board here. It worked for me.
There may be other factors at work here if there are I'm sure someone else will point them out