When you feel that way, do you test your bgs? It could be a sign they are very high or very low. Does this seem to happen at a specific time of day like after lunch. It could be that if you are insulin resistant and if you eat carbs your body is producing too much insulin which gives you that feeling. If I eat grains, I tend to get that sleepy feeling, so I avoid them. Trying to keep bgs fairly stable all day will avoid those problems.
When my bgs get high I feel warm all over, somewhat intoxicated, and often suddenly very, very sleepy. This is why much of my carb impulses take place just before bedtime. For years it seemed the perfect cure for the end of a rough day and the beginning of a sleepless night. Too bad it isn't. Ha ha God, very funny.
This sound obvious, but are you getting enough sleep? As the week goes on, I start feeling more and more tired. When I sleep in on Sat, I feel more alert. I seem to need more sleep than the average person. I guess that is from the years on DM wearing on me.
I work Monday thru Friday from 7 am to 4 pm. So I go to bed at about 12:30 am and get up at 5:45 am. On the week end, I go to bed about the same time or later if a good movie is on and wake up about 7:30. Sometimes I go back to sleep for a cat nap about 10:30am.
I have a real hard time telling when I am high, low or normal unless I test. Sometimes I swear I must be low and test and will be 120-130. Do you usually feel this way several hours after eating lunch? If so what you may be feeling is the result of your pancreas putting out too much insulin.