Immature nervous system? Scared

Hey guys my little one is about to be 6mo old

We were holding her facing outwards and my husband was like squatting up and down

She got excited then got like stiff and kinda shaky.

I’m scared out of my mind because she has never done that before

Could she have just lost balance?

He was holding her but the butt and had his other arm wrapped around her

Or was she excited?!

It lasted maybe 3 seconds

Seizure?!

Help :/ anyone with experience

Her appt isn’t until August 10th