Tired after carbs, but fine after sugar

Background: 27F. Keto for 2 weeks. Waiting for C-pep results. No medications or insulin at this point.

I did a small experiment to see how my body reacts to sugary food vs. carbs. Had pasta with my lunch one day and became very tired and groggy about an hour after. A couple days later, I had a big slice of ice cream cake for my birthday. Felt completely fine afterwards.

Anyone with similar experiences? Maybe you have a glucose monitor so have more info on what happens after consuming carbs vs sugar?