See below. Am not familiar with "unspecified", but transient cerebral ischemia means diminished blood flow to a part of the brain causing clinical symptoms. Since this can be the first sign of an impending stroke, this needs to be fully evaluated and medication started for prevention. See a neurologist and get this fully addressed.
Cause unclear. There is brief, diminished circulation to the brain without a clear cut cause (like a cardiac arrhythmia or blocked neck artery) that is responsible for the symptoms being investigated. The term is vague and unsatisfying so it's understandable if you're still in the dark.