Sugar crash
"The sugar high is all fun and games until the resulting sugar crash affects the quality of your day.
The term refers to the sudden drop in energy levels after consuming a large amount of carbohydrates. This can include pastas and pizza but is usually more common after eating simple carbohydrates, also known as simple sugars, such as desserts.
A sugar crash often causes undesired symptoms that can disrupt productivity and energy levels throughout the day."