Ways to mess with Characters heads

[Surgebound Rainspren he/him]

I am currently writing a short story called "My Small Reality" and I need some help.

the premise of the story is the character is the only thing really exists. he is the Alpha so to speak. But parts of his sub-conscious have become sentient as a result of a massive shift in his ideals. these broken of bits are slowly gaining more and more control over his reality. so I need ways to mess with his head and make him doubt reality. But I have no ideas about how to do this and really need some help.    

[Lindel he/him]

The concept sounds intriguing, but I think we need a bit more context before we can understand exactly what you're asking for. 

[Surgebound Rainspren he/him]

the "pieces" (named: Beta, Gamma, Delta, Epsilon and Zeta) are slowly gaining control of reality. the alpha is losing the control he never knew he had and his reality starts to alter. So I need ways to that would completely change normal reality.

[Lindel he/him]

Okay. I sort of see where you're going with this, but I think it would really help us help you if we could get more than two sentences. To start, what was the setting originally like, before the shift? 

[mail-mi he/him]

Voices inside his head are always options.

[Delightful]

Shifting gravity, the same people randomly appearing all over the place, colours changing, sounds coming from the wrong directions? I'm thinking of Inception.

[Steel he/him]

Voices in his head distract him from survival/reality, forcing him to accept them to stop them from destroying himself?

[Truthwatcher Ferring]

How about having his fears, insecurities, or dreams become real? It would be funny if they suddenly got a celebrity boy/girlfriend or became an astronaut. But maybe you're thinking of something more subtle.

Edited October 9, 2014 by Truthwatcher Ferring