It means "astonished". Random House Dictionary 2009 has: "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."
(The idiomatic phrase "to be beside oneself" means to be anxious, upset or disturbed.) "After my dog wandered off, I was beside myself with worry."
To be beside yourself means to be overwhelmed with emotions, usually negative ones such as anger, frustration, or disbelief. It suggests a feeling of being unable to control or cope with the intensity of what one is experiencing.
The phrase "beside oneself" dates back to the 16th century and means to be overwhelmed with emotions like anger or excitement that one seems to be outside of oneself. It implies being out of control and disconnected from one's usual rational self.
To disentangle oneself means to extricate oneself from a complex or difficult situation, relationship, or problem. It involves freeing oneself from entanglements or complications.
to bathe oneself
to find oneself
happy
It means beside.
happy
"Cortarse" in Spanish means "to cut oneself." It can also be used to mean "to cut off" in some contexts.
hes trying to get your attention or hes just walking beside you
If you think about this for a minute, you can figure it out. An idiom is a phrase that doesn't make sense when you think about it literally. Can someone actually stand beside themselves? That makes this an idiom.