What Happened to Dr. Smith?

As we all know, Dr. Zachary Smith started out as a competent person working for the space program, presumably a medical doctor since he gave the Robinsons a checkup before they boarded the Jupiter 2.

And Smith was also hired by an unnamed sinister foreign power to sabotage the flight of the Jupiter 2. and thus kill the Robinsons and Major West. And Smith did a competent job of sabotage, at least up until he got trapped aboard the Jupiter 2 and was launched into space with the Robinsons.

During the first five or so episodes of Lost In Space Smith occassionally tried to kill one or more of the Robinsons, even after they crashed on some unknown planet and had very little chance of ever reaching their goal Alpha Centauri. Presumably even if they did ever reach Alpha Centauri it should be long after the unnamed sinister foreign power sent expeditions which reached Alpha Centauri.

But Smith changed after the first few episodes. Instead of remaining evil and competent, Smith became much less of each. Instead of trying to kill the Robinsons, Smith generally considered himself a member of the party and helped a litle, even though he was selfish, greedy, and lazy and often caused various problems for them. And Smith was much less competent.

So what caused the big change, in universe?

And my guess is post-traumatic stress disorder PTSD. Smith was not chosen to go on the flight and thus he was not chosen for his pyschological abilites to hand the stress of the dangers of space. So maybe the Robinsons and West enduring even more terrifying dangers in the first few episodes without being traumatized by them, but Smith couldn't take the dangers he faced.

Or perhaps some event early in the series happened off screen and was never seen in any episode that terrifed Smith and reduced him to a nervious wreck who couldn't stand danger and realized he needed the Robinsons to survive.

Since the new Smith would do anything to avoid danger and confontation, he no longer threatened the Robinsons and did his best to cooperate and placate them, but was no longer competent enough to avoid causing trouble and facing more stress.

And possibly Smith suffered some damage to his memory in that hypothetical off screen incident, and so was no longer able to remember what actions were mistakes, and so kept repeating those mistakes over and over again.