Is it normal for blood sugar to go down to 4.7mmol/l 1 hour after eating a big meal?

Yes, if you're not diabetic, my friend, but the big question is, why are you testing after 1 hour after eating ... unless you happen to be pregnant or a newly ddiagnosed diabetic who's been requested to test after 1 hour so that you can see what effect various types of food(s) and/or drink have on your blood sugar (glucose) levels. You would normally test two hours after eating as it may take this long for your body's digestive system to break down the food and release the glucose into your bloodstream.

yes.

s[pecial;l;y if the meal ws propery nutritious, fileld with ptoeisn instad o sugars