From the question it appears be seen as a problem, therefore, I presume that the causes for the same would have been examined and the need to check whether it is misconduct stems after no merit is found in the cause for sleeping at work.

The nature of contract between the employee and the employer organization is that employer has hired the employee for work return for consideration in the form of remuneration and benefits within the service conditions of the contract.  Therefore, sleeping while on duty goes against the nature of the contract and calls for corrective action.  Corrective / Disciplinary action is essential not only to eliminate the issue but also as a clear message from the organization to all employees as to what the organization expects.

As per the applicable standing orders, sleeping on duty is a misconduct. 

Even if there is a cause for sleeping while duty is found to be acceptable, clear communication should be made to the employee as to what the organization accepts from such employee under such circumstances and that such behavior if repeated would be unacceptable.  It is also important that all employees also understand the consequences of such behavior.

 As  far as I know, sleeping during working hours is a serious misconduct. But, it also depends on the employer's policy.

  Employer pays you for work not for sleeping, so obviously  its a misconduct.

But, if many of the employees at work in an organization look sleepy then it means that its just not the fault of employees but the organization is lacking to provide a passionate and lively work environment.There are many factors that count in creating an environment lively for work and also employee physical health, passion towards work etc. count in this matter