Take time to gauge the temperament of the class. If you notice any unusual behavior by a particular student in the classroom, observe the student for some time to see if the behavior prolongs or if it is just a passing cloud. Talk to a trusted colleague to know if this behavior is evident in other classes as well. It is important to use your discretion when talking to co-workers. The intention is to help the student, not start a gossip chain.
If you notice that the behavior lasts for longer than usual, invite the student for a private chat and:
In some cases, the student may be in denial or may not open up to you at all. In such situations, leave them alone and quietly observe them for a few more weeks, before approaching again. Remember, a student can never be coerced into confiding their problem. A good thumb rule is to attempt twice and if the second attempt fails, notify the campus counselor and let them decide on the best approach.