This is your blood glucose level dropping rapidly, also called a sugar crash.
If you’ve had a glucose spike which then rapidly drops back down, you are seeing in real time what is commonly known as a blood sugar crash.
When lots of glucose is quickly released from food into your system your body works really hard to get it back to a stable level by producing insulin. This rapid reduction in blood glucose can cause hunger and cravings, making it harder for you to reach your weight loss goals.
Importantly, don’t be tempted to eat to bring your line back up. Give your body some time, and you will see it naturally works to return to a stable level, by accessing the stored glucose already in your body.