Dear Navjot Thakur,
There is a mismatch between the heading of your post and the main body. Secondly, I wish you had provided information about the nature of your industry, the department in which the employee works, the length of service of the employee, etc.
"Mood swing" is a mental health issue and requires treatment from a certified psychiatrist. On the contrary, complaints about the quantum of work, the tendency to jump into light, etc., are behavioral issues and counseling may be sufficient.
Why does an employee feel that the quantum of work is excessive? What is the take of the reporting manager on the complaint of the subordinate? Is the quantum of work the same for other employees also?
Are you comparing the work done by the employee's predecessor? Occasionally, such comparisons don't work as there is a basic difference between human beings, and work done by all may not be identical. Some leeway for variation has to be given, but the leeway may not be major.
Thanks,
Dinesh Divekar