Final answer:
Sudden changes in behavior may indicate underlying mental health or substance use challenges, pointing towards possible addiction or dependence that might require rehabilitation.
Step-by-step explanation:
The early indicator that an individual is experiencing a mental health or substance use challenge among the options provided would be c) Sudden changes in behavior. Such changes can manifest as imbalance and posture problems, difficulty with planning and executing tasks, poor judgment, or personality changes. These symptoms indicate that an individual may be developing dependence or addiction, where sustained use of a substance leads to physical and/or psychological reliance. Furthermore, mental health conditions can emerge due to life experiences, genetics, or as a result of substance abuse. It's important to remain cognizant of the effects of psychoactive substances, as the rewarding experiences like euphoria or increased alertness can eventually lead to addiction and rehabilitation needs.