I'm trying to remember an old sci-fi novel. I'm sure it was no later than 1980.
The plot:
The novel starts with the alien being banished to Earth, as a punishment for some crime he committed.
He doesn't have a physical body per se. But, he inhabits and take over the body and mind of a human, animal or basically any sentient creature.
This is similar to the movie, The Host, minus the romance and the host's ability to resist the control.
The alien takes over only if the Host is asleep.
The alien starts with taking over a cat. It realises it's not the master, makes the cat commit suicide, moves to a dog and eventually takes over the minds of a human.
The alien targets scientists because he wants to return back toto his home planet.
The chief scientist, a man, decides to stay up to fight back. He and another scientist, a woman, are the last. He dozes for just a second and the alien takes over.
When she doubts him, she ties him down to prevent another suicide.
Does this sound familiar?
Sadly I don't recall the cover nor the Publisher as I was just a kid.