Loss of consciousness can signal a serious cardiac problem.
Sudden fainting or collapse may occur when the brain temporarily receives less blood flow. While fainting can sometimes have minor causes, it may also signal a serious heart rhythm problem or other medical emergency.
Warning signs before fainting may include:
• Dizziness
• Blurred vision
• Nausea
• Rapid or irregular heartbeat
If someone loses consciousness, even briefly, it is important to seek medical evaluation.
If the person does not wake quickly or appears unresponsive, immediate emergency care is required.
Emergency Action
If someone collapses, loses consciousness, or is unresponsive, call 911 immediately.
Source
American Heart Association