Couple of things here...
Yawning can be indicative of improper breathing. Anxious/hyperventilation type breathing can happen without us realizing it...and one of the more subtle signs can be yawning, in an attempt at getting O2/CO2 levels corrected. Try doing some breathing exercises when you catch yourself yawning a lot for no reason.
The other thing this could be is a reactive hypoglycemia episode. Eating a lot of simple carbs, such as pancakes will raise BGL quickly...
...but then they can plummet, leaving you feeling shaky, weak, fatigued, sweaty and anxious.
Most of the time this is an isolated incident, related to a heavy simple carb meal...but if you continue to see a pattern, you may want to discuss this with your doctor to get a blood glucose test run.
Bottom line, this is probably a one and done type of situation, and you needn't worry.
Hope you are feeling much better today!
"Courage is not the abscence of fear, it is feeling afraid and doing it anyway!"
"Worrying does not empty tomorrow of its troubles...it empties today of its strength."
Corrie Ten Boom
Panic Syndrome recovery due to CBT