It is possible to aspirate food into the windpipe at times. I doubt this is the case with you. You would probably be very uncomfortable and coughing your head off if you had a sunflower seed into your bronchial tree. If you have any suspicious symptoms then you can get it checked out.(I've known of cases where a person swallowed their on tooth) If you have no discomfort and no unusual cough then I think it is very unlikely that you aspirated the seed.
I hope this information helps. Follow up questions are welcome if you have any.
Anthony Bray MD
Potentially dangerous. If you did aspirate an object such as a seed then a pulmonologist would do a bronchoscopy and retrieve the object out. As I said if you feel comfortable and not coughing then I doubt you aspirated. If you aspirated an object then it could be a set up for an aspiration pneumonia as one potential complication.
I hope this helps. Further questions are welcome if you have any.