If you feel unwell at altitude it is altitude illness until proven otherwise.
Never ascend with symptoms of AMS.
If you are getting worse (or have HACE or HAPE), go down at once.
If you hire your own porters, please be aware that they are just as susceptible as you to the ravages of AMS. Porters may even be at increased risk of severe forms of altitude illness as they are unlikely to know anything about AMS, are more likely to have a communication barrier to telling you how they feel, and may actively hide their symptoms as they fear losing their job due to illness.
For those of you who will be trekking in Nepal, please look at the AMS questionnaire with phonetic Nepali translations (based on the Lake Louise AMS scoring criteria). For more information, also look at the International Porter Protection Group's web site.