Maquilina:
Please do be careful. My old Peugeot would do this to me almost exactly at 30 MPH if I was pedaling hard to hold the speed, so I got very used to dealing with a resonant wobble. On the Peugeot I could stop the wobble by pressing one leg against the top tube. There may not be anything "wrong" with anything. It may just be that things add up to being unstable when you bump them like that.
The recent incident was on my Lynskey R350 which is not a flexible flyer by any stretch of the imagination. The front wheel is from Light Bicycle and is a 46 mm rim brake wheel built on a Carbon Ti hub. Nothing dodgy in the front end. Cane Creek Headset in good condition. Oh, I was about 245 pounds when this happened.
This wobble started at about 25 MPH. It showed up in a group ride. I am afraid that I scared the <expletive> out of the guys who were riding right behind me. The leg on the top tube worked to damp the wobble; I do that reflexively thanks to my trusty old Reynolds 531 steel frame wet noodle of a Peugeot.