According to the documents, obtained by TMZ Sports on Thursday, the ex-MLB player was struck in the head by a baseball while working as a pitching coach in August 2021.

The accident caused a serious injury -- investigators say he suffered a fractured zygomatic bone, and required surgery to fix the issue.

But, according to the report, witnesses told them that in his recovery from the injury, Giambi became "very emotional, very negative and would let the smallest things ruin his day."

Another witness, according to the docs, had described Giambi as "very emotional, depressed, and paranoid" in the months following the surgery. It was noted Giambi "had scans done and saw a neurologist but was not diagnosed with anything."

Giambi -- the brother of ex-MLB star Jason Giambi -- killed himself roughly six months after the injury on Feb. 9 at his parents' home in Claremont, Calif. Officials said he left a suicide note at the scene.

Investigators wrote in the docs that Jeremy had a past history of drug use, but he was not believed to be abusing any drugs in the months prior to his death. Lab results show he had no alcohol or drugs in his system at the time of his passing.

Jeremy -- who played six years in the MLB and gained national fame for his time as an Oakland A -- was just 47 years old.