Strange Betta fish behavior?

Kudos for removing the plant immediately.

"Freaking out" can be caused by ANY sort of irritation not just parasites. Bad water quality for example: as the ammonia burns the gills and the skin, the fish will try to get rid of the burning feeling by scratching, flashing, sudden bursts into swimming. So before nuking your tank with RidIch or something similar, get the water tested (and ask for the exact readings - most pet store employees couldn't analyze a water test if their life depended on it).

bettas will drown if they can't get to the surface to BREATH. anything that a betta could get stuck in should be removed.

silk plants and most real plants are best. avoid plastic and anything with sharp edges, anything his fins could snag on.

as to why he was freaking out, not sure. thrashing about wildly could be a disease called ick, which is treatable.

And Alppha fish showed up

try adding aquarium salt (1 tablespoon per 5 gallons) to prevent any infection and strengthen the immune system. a 25% water change and temperature of 80 degrees will also help.

http://bettacare101.com/diseases