This happen to my lo when he have not enough sleep during the day or played too much. Too tired and gets v cranky.
Does he sleep alot in day time? as 18mo, I think one nap around 3hr nap is enough.
Is the room temperature same as per normal? Recently the weather is kinda warm which will also effect their sleep.
Normally I will feed my lo w water/milk and he will go back to sleep.
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