I am very sorry to hear that you and your husband had this experience, which sounds quite frightening.
Whenever people develop sudden symptoms like this, especially while exercising, the job of the emergency room doctors
is to make sure the symptoms are not from something life threatening like a stroke or a heart attack. It sound like this has been done already, so that is reassuring in a lot of ways.
Additionally, the chances that this is a very serious problem are lowered by the fact that your husband is young and healthy with no known medical problems.
There are several common reasons still for young, healthy people to get lightheadedness and other symptoms during exercise. These include overexertion and dehydration, and in these cases the symptoms typically resolve with drinking fluids and resting. Dehydration in particular can cause other odd symptoms, including a cold sensation or numbness
I suggest that your husband make an appointment with his primary care doctor
right away for followup from the emergency room visit. His primary care doctor will be able to perform a more complete physical examination and help determine whether any additional work up is needed at this time.