Ketamine side effects re-surfacing

My brother is going through infusions now (3 in last 6 days) yesterday was his last one, later that night he was recovered and acted normal, and earlier today was acting normal.

However later in the day (today) his speech has become extremely slow, has anyone seen or know why this side effect would resurface a day and a half after him not experiencing it?

He has also gone into an extremely depressive state of mind alongside the same time frame with the slow speech