The two terms can be confusing, as they are often times used interchangeably. The main reason why I use the term "hypnosis" on my website is for legal reasons, as the term "hypnotherapy" is reserved in some countries, for doctors, because of the term "therapy". In France, individuals can refer to themselves as hypnotherapists, even if they are not doctors.
Beside that legal reason, the two terms refer to the same state of mind and type of consultation. Unless you are diagnosed with certain forms of mental illnesses, such as schizophrenia, a hypnotherapist would provide the same service as a hypnotist.