If an investigator that has 0 sanity has one of the insanity traumas that require 0 sanity played on him and then he heals and is able to remove 1 horror, does he lose the trauma or does it stay with him even though the sanity requirement is no longer met?

Can somebody answer please?

The trauma stays unless it specifically states otherwise. The number at the top denotes the remaining Sanity required to initially play the card on the Investigator (in this case 0). The trauma remains until healed by some other effect (e.g. Sedative). A good example of this is the trauma card Delusions of Grandeur, where it has a requirement of 4 Sanity and allows the Keeper to heal one Horror from that Investigator to gain a threat, but is removed when that Investigator has no Horror left. It specifies the removal because the standard rule is for the trauma to remain, regardless of remaining Sanity.

Hope that helped!

Awesome. Thanks for the answer and for the perfect example card. That cleared everything right up, thank you.