Be beside one’s self
(PW) be very upset
I was so mad when I heard that she was making up stories about me that I was beside myself.
(MW) in a state of extreme excitement
(dictionary)
almost out of one's senses from a strong emotion, as from joy, delight, anger, fear, or grief: He was beside himself with rage when the train left without him.
(freedictionary) beside oneself (with something)
Fig. in an extreme state of some emotion.
I was beside myself with joy. Sarah could not speak. She was beside herself with anger
to feel an emotion that is so strong it is impossible to control He was beside himself when she didn't come home last night. (often + with ) We were beside ourselves with excitement as we watched the race.
extremely upset or excited My mother was beside herself with curiosity.
(yourdictionary)
wild or upset, as with fear, rage, etc.
(thePhraseFinder)
Beside himself. Why do we describe a distraught person as being 'beside himself'? Because the ancients believed that soul and body could part and that under great emotional stress the soul would actually leave the body. When this happened a person was 'beside himself.' This same thought is to be found in 'out of his mind'; and in 'estasy' too. 'Ecstasy' is from the Greek and literally means 'to stand out of.'" From "Dictionary of Word Origins" by Jordan Almond (Carol Publishing Group, Secaucus, N.J., 1998)
