I had similar problems. I would get to 2pm and crash like a computer shutting down.
I made some changes to my diet and reduced my carb intake at lunch time,
I would always be 4.8 to 5.5 before lunch, but what I was eating would spike my sugar to high 8 to 9.
As I'm diet controlled and have a desk bound job, this was enough to trigger the sleepy bug.
So I reduced my gluten intake and cut out crisps of any description.
So a nice salad, with salmon, or egg.
Followed by a bag of popcorn, washed down with a peppermint tea (to aid digestion) instead of diet coke.
In the evening to help me sleep at night @ 9pm I stop drinking tea or coffee and have camomile tea. By 11pm it's as much as I can do to keep my eyes open.
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