[bks]

In life, we all have blind spots. Things that are obvious to others with more experience but may be invisible to ourselves.

But it may have been a helpful suggestion from the manager based on observation or personal experience that the OP might have some attention deficit issues that may or may not be improved with medication.

Hanlon's razor may apply here also.

[paloaltokid]

It doesn’t matter if the manager was intending to be helpful. You don’t suggest to an employee that they start taking drugs, full stop. The furthest you can go is to suggest medical diagnosis.

[Nursie]

Take stimulants so you can work harder for us. Yup, just some friendly advice.

However well intended, it's so wrong.