Conversation so far:
What is Haunting Matt Parkman by Sylar?
Matt Parkman, regretting his actions, is haunted by Sylar, who claims to have lingered in Parkman's mind after Parkman sucked all his memories and replaced them with Nathan's.
What does Sylar do to Matt Parkman?
Sylar escalates his tormenting of Parkman, using his own telepathy against him to force Parkman to use his powers to save himself.

Question: How does Parkman react to the haunting?
Self-contained rewrite: How does Parkman react to the haunting and tormenting using his own telepathy against him