Leonard is not lying FFS!

I keep seeing people considering that Leonard's condition is psycological and he's lying, even to himself.

That's not possible. Watch again the scene he beats Natalie. She just says everything to him, makes him angry so he beats her, and a couple minutes later she comes back and talks him into believing it was the other guy who did that.

*He actively forgot what he had done 2 minutes ago!* That's the definitive proof.

Also, look at when he opens his truck and takes the bullets. He doesn't remember it was his, and that the bullets were put there by him because he didn't wanna kill anybody. And just after he kills Teddy.

The condition being psycological was his believing about Sammy. Sammy got the desease and received the money, and Leonard investigated him trying to prove Sammy was lying for the money. Leonard accused him.

Then Sammy's wife went talk to him. She wanted to believe Sammy could come back. She wanted a definitive proof either that old Sammy was gone, or that he was lying so he'd stop it and come back.

A definitive proof wasn't available, so she decided to make the final test. She died. So, in her doubts, either Sammy chose to kill her to keep the lying and the money, or he was indeed ill.

This psycological condition has NOTHING to do with Leonard! Leonard said himself he was wrong, because after the death he starting believing that Sammy was indeed ill.