Non diabetic. blood sugar went to 65 4 hrs after eating. always in the 70-90. what can cause this?

I don't consider the cited level worrisome. It likely means your bodies' metabolism factors are delayed is bring it into the usual range. I doubt it has any significance.

As long as you did not have any symptoms of weakness or lightheadedness, and otherwise felt OK, a blood sugar temporarily down to 65 should not be a major concern. If you are having symptoms, however, you should see your doctor. How did you happen to have the supplies on hand to check your blood sugar frequently if you are not diabetic? Good luck.

A blood sugar under 70 is considered hypoglycemia. In your case this low reading after eating could be reactive hypoglycemia if you had a carbohydrate rich feeding & especially if sweets were involved. Your blood sugar may have spiked causing release of insulin to lower it & it brought the sugar level too low. Apparently you had no symptoms. An oral glucose tolerance test can detect such reactions