I know from my own experience that possession is real. I am not going to try and convince anyone that they are suffering from demonic possession. That is something you will need to realize for yourself, perhaps in connection with a spiritual advisor if you have one. I will say it is possible to be possessed without realizing it. For those who do not believe in the reality of possession I recommend M. Scott Peck's book "People of the Lie".
I do not wish to be like the man who sees someone drowning in the lake yet does not stop and throw a lifeline. And I do know how terrifying it can be to realize you are dealing with an evil spiritual entity, something that most of the world does not even believe exists.
The Catholic Church has been making a concerted effort to train more exorcists. This effort is detailed in the book, "The Rite: The Making of a Modern Exorcist." I do not know at this writing how many exorcists are currently active in the Catholic Church, but that is one avenue where a person might seek help.
In order to perform an exorcism a person must be given authority by God to do it. It is a relatively rare gift. I personally have known only two exorcists in my life. I have seen about a half dozen exorcisms performed.
There is also such a thing as self-exorcism. It is accomplished thru prayer and meditation. It requires more faith. For those who wish some guidance in the matter you may contact me directly at firstname.lastname@example.org. Please describe the conditon or conditions that make you suspect or know that you are possessed in a short letter. Put "Possessed" in the subject line of the e-mail. I will answer all e-mails and try and provide some guidance.
Yours in Christ,