Can I be hypnotized against my will?

In general, no. Hypnosis requires your participation and consent to work.

There are "shock" inductions that can be performed that startle the subject into hypnosis, but without participation and consent, the subject will pop right back out again in less than a second.

A very skilled hypnotist can make involuntary hypnosis last longer, but you would NEVER find that in a therapy environment where trust means everything.