After a big meal i feel weak and tired. could this perhaps be a sign of diabetes?

Fatigue after meal: Fatigue after eating may be normal in some cases, such after an especially heavy meal. This can last from 30 minutes to a few hours. There may also be a relationship between fatigue after eating a low thyroid levels. Diabetes not as much so, although both diabetes and low thyroid conditions can cause symptoms of fatigue in general.