can cause fainting
attacks. In his case , it is possible that he could have had a hyperglycemic attack as he is also on prednisone(steroid) and steroids
are known to cause an increase in blood sugar levels.
How is your father's Blood pressure? Is he hypertensive? If yes,high BP could be another cause of fainting.Low BP/Postural hypotension
can also cause fainting.
Cardiac conditions can also cause fainting.
Or it could be a vasovagal syncope which happens while standing for prolonged period under the hot sun.
Most likely, cause is hyperglycemia (increased blood sugar levels ) as his blood sugar levels were 400 at the time.
Please consult his physician as his medication dosage may have to be adjusted and he needs a throrough cardiac evaluation .
Hope I have answered your question.
Have a nice day :)