Your trainer is a special person in your life.  They may in fact know you better than any of your friends. If you have one, your trainer has seen you in a light that most people have not.

you show up with no make -up on(ladies), are not fully awake yet or are stressed from your day. During your session some sort of weaknesses is exposed as you try to challenge a new exercise you’ve been given (How dare anybody find out my right ankle is not as strong as my left).

But you should thrive on that challenge and by the end of the session you are most likely full of sweat and have a beat red face.  Wow, who wants to be around me when you’re like that? Your trainer of course.  Your trainer is there to support you no matter
what you look like or how you act or how you occasionally whine
and grunt(yes that noise you hear when people are at the very end of
their work-out set). You clearly feel comfortable enough with this
person to allow yourself to be exposed in such lights. (If you are not
this relaxed and at ease with your trainer I suggest you high-tail it
to a new one).

This comfort level has freed you to tell you trainer a great deal about
you life, from the exciting things you have going on to the stressful
“what should you do” moments in my life. No matter what, you trainer helps
me feel at ease.  He or She also calls you out when you should be taking better
care of yourself, for instance sleeping more.

All of these things improve you mental health as well as my physical.  Both facets of health are equally important.  There is a reason why you feel so much better after you exercise and after being around positive people.  So for those of you who have a trainer or someone similar,
thank them for positively impacting your life.