When someone is semiconscious, they are only partly awake and aware of what is happening around them.
Being semiconscious is not good because you might not be able to understand or respond well.
Examples:
After the accident, he was semiconscious and couldn't remember what happened.
She was semiconscious after the surgery and couldn't talk.
The medicine made him semiconscious for a while.
The baby was semiconscious after waking up from the nap.
He felt semiconscious after hitting his head.
The dog was semiconscious after being sedated at the vet.