3. I seldom participate in risky or dangerous sports/activities (e.g. water skiing), but I was injured on one occasion while playing such a sport. Is such an injury considered as an "accident" or "self-inflicted" or a "negligent" event? Will it affect my claim for medical or accident insurance?

As discussed under the subject of "exclusion" clause, the main issue is whether or not the particular sports that you have participated in is an excluded coverage. If yes, the insurance company will not pay. If no, you can submit a claim which will likely be admitted.