Running a business will involve both physical and emotional activities. Even in the planning stage, you will have to consider every single thing; business planning, operational process, accounts and procurement, as well as products/services marketing. It is totally tiring and stressful.
Having good physical health will ensure you the strength to cope with all heavy activities and operations involved, supported by good emotional health that will avoid you from being demotivated by any unwanted problems and challenges. Having a proper planning and back-up will help you to be ready and steady. It is okay to feel down and stress sometimes but you have to ensure that you have the time off to refresh.