That is 100% correct, anyone who becomes dizzy during exercise should see their doctor. You haven’t given us much to go on though. Does this person get dizzy with any exercise or is it specific exercises? I can tell you that it is fairly common for people to become dizzy when rising from an exercise that is done supine or prone (or semi-supine/prone) and then standing up quickly or relatively quickly (relative for them). This is common for people that use a leg press machine that has them sitting or sitting reclined. The big muscles of the legs are demanding a lot of blood flow. The circulatory system “shunts” blood to the legs and decreases blood flow to the upper body (and head). The blood is down in the legs and person stands up. The blood pressure in the head is a little bit too low. The brain just knows it wants more blood to the brain. Quickest way to accomplish that is to make the person sit down again or fall down if necessary. Check with a doctor, definitely. It could be more than just postural hypotension. But also instruct the client not to get up right away, allow their breathing and heart rate to return to near resting levels, and get up more slowly.