My boyfriend has been moving furniture all day and he just got done then he told me that his head is pulsing and it's hot. why is that happening?

May be dehydrated.: Check temp to be sure it's normal. Fever can be due to an infection and "heat stroke" can occur in young people. Next, if a BP machine is available, check the BP sitting and standing; if dehydrated, ones BP might fall with standing. Of course, the treatment would be drinking plenty of water. Occasionally the symptoms are from high BP in which case a visit to ones doctor is warranted.

Dehydration: He probably is dehydrated. Tell him to rest and to drink a lot of water. If he has any chest pain as well he should see a doctor