To help save you from endless hours of frustrating Internet searching, here are links to sources of consumer health and wellness information that have been found to be most reliable (i.e. authoritative & produced by experts), while being understandable to a wide audience, easy to use and navigate, and incorporating the latest research findings.
In order to research your health-related topic in a greater depth or detail, be sure to consult the many useful online medical encyclopedias, dictionaries, books, and research articles you can access via the corresponding tabs on this guide.
Note that this is by no means a comprehensive list of consumer health information sources (a wider range of sources can be found on the website of the Medical Library Association), and that none of those listed claim to be a substitute for professional medical advice. Also, bear in mind that sites have different strengths and weaknesses--for instance, some offer useful links to medical research literature, whereas others offer the opportunity to ask questions or share experiences in discussion forums. Also consider searching your topic in more than one resource, as the depth or breadth of information offered likely varies.