What could cause our toddler's strange episodes of acting up?

Question

Background:
Our son is almost 3 years old. Normally he is well behaving, speaks in sentences, shares toys/treats with other kids nicely, willing to sit down and learn letters etc.

Problem:
A few times in the past two weeks he had these crazy episodes where he is acting absolutely out of character. He cries about the smallest possible problem and a second later he is laughing at virtually nothing. He demands things by shouting, will not hold eye-contact, becomes restless and won't sit still for 5 seconds if not held, throws things around, blabbering without any meaning and making faces, doing the exact opposite of what he was told to defy his mother. It normally lasts hours and normally it is finished when he goes to sleep.

Question:
What is this (or what is causing it)?

I tried reading some articles but nothing that I could find fits this.

What we considered:

• he ate some heavy sugary stuff before today's episode (badly executed bribery, our fault)
• the childcare he goes to 5 days a week has just got a new baby who is only 6 months old and our son does appear to be jealous of the attention he gets from his favorite teacher
• he was sick for a few days recently with lots of coughing and insufficient sleep

Answer 1

To me, this doesn't sound like particularly abnormal behavior for a three year old. Bursts of excessive, playful energy, nonsense babbling from a child who can talk, occasional boundary testing, demands and defiance, and emotional volatility are all pretty much standard three year old things. The one thing that seems a bit unusual is that these all occurred at once in the form of a distinct episode. If you feel that your son is literally unable to control these behaviors or if he (or the rest of the family) is very troubled by the intensity of the episode, it would be reasonable to ask your child's doctor.

In what I suspect is the more likely case, your son is just acting out because he's overwhelmed, overstimulated, or has excessive unburned energy. Some possible causes to consider are:

• Overtired or overstimulated, needs an earlier bedtime or some downtime during the day
• 'Undertired', needs more outdoor or active play to burn energy
• Has an emotion he doesn't know how to express or process (jealousy the likely possibility)
• Needs attention or connection, and doesn't know how to ask for it
• Wants/needs more choice in his day, so he's taking some control by force
• Feels some minor physical discomfort that is making him restless and uncooperative
• Acted up once for no particular reason, and you reacted strongly, so now he's experimenting with recreating the reaction
• Going through a period of rapid learning, and having trouble 'winding down' his excited mind
• A less likely possibility could be a food allergy or intolerance, which in uncommon cases can cause hyperactivity

The fact that it seems to end as soon as he sleeps points me towards the first two as the most likely possibilities.