Agree with everyone about there being a reason, it just might not be apparent without a little observation of self. Exhaustion and/or low energy could be attributed to diet, thyroid, lack of sunshine or even sometimes too much sunshine, or too much of one kind of weather, that affects one's moods... being with people, especially those with lots of energy (children) can give us a buzz, but if we're not regularly used to this, a phase of activity can be balanced with a feeling of tiredness.

especially after an adventure with the grandboys

never without a reason

Usually when my headaches are never ending.

I hate having no energy for absolutely no reason

a few times a month

For me, there is always a good reason, such as sleep deficit or carbohydrate excess (glucose intolerant) - or else I have some kind of 'flu (which isn't too often).

ughhh almost always

Always

Always