My starter doubled in size in the first 5 minutes or me creating it?!

I decided to create a starter and it started rising immediately and it doubled in size within 5 minutes or me and it’s dropping now. I’ve only done this once before years ago and I don’t know if this is supposed to happen. I did a 1:1:1 ratio and my room temperature is about 72ish degrees. I did plenty of research before starting but I don’t know. Is this a good or bad thing? Help!