Feel under the weather
It means to feel sick. In most cases, it's used to say that you feel a little sick. ... But… you usually feel low on energy and feel tired when this happens. To be Sick and ill both mean to feel unwell.
I feel under the weather today.
Feeling under the weather
To feel indisposed
I understand that Mr White is feeling under the weather today, so you folks are going to have to be making do with me today.