Is it ok to take half of a 25mg valdoxan tablet? 25mg too much for me and less then a half tablet still healp me sleep.

Your prescriber will have to know/approve as other than sleep there may be intended effect on depression and/or anxiety. Otherwise, you are doing the right thing by adjusting down your dose in case undesirable side effects.

Valdoxan/ agomelatine is not a medication that is approved for use in the US, thus I have little familiarity with it. However, I am reading that it is a "coated" tablet. Coated tablets are usually not designed to be cut. Please contact a local pharmacist in Denmark who can give you more specific guidance.