Brushed teeth 2 days ago. Some tooth brush bristles fell out, I swallowed. Now I feel sick and can't eat. Some pain on right side.

Answered incorrectly. Sorry i must have misread this earlier. Bristles falling out is not likely to cause a problem if swallowed. Anything is possible however i think it would be an unlikely source of your discomfort. You should have a physician examine the pain on your right side.
Probably unrelated. Toothbrush bristles should pass right through. If your probably unrelated gastrointestinal symptoms persist, see your Physician or seek evaluation Urgent Care (not ER). And please replace your toothbrush every 3 months so that this doesn't happen again.
IN YOUR HEAD. Toothbrush must be old if bristles fell out.Get a new brush and use it and the pain will go away and then eat.