The number one fear seems to be dining alone. Other fears are safety and loneliness. And people feel self-conscious about being alone when everyone else seems to have a companion. In fact, I find that many people reach out to a solo traveler. Define the kind of vacation you want, then look for a trip that fits.
Resorts are tough, especially romantic resorts in the Caribbean.
And car trips alone can be quite stressful in unfamiliar places, with no one to help with reading maps. Because you immediately have something in common with the other participants. I like trips with small groups and a common focus. College campus vacations such as Cornell U's summer Adult University are easy alone, require no books or homework, and leave plenty of time to enjoy the area with the new friends you've met in class 2. Learning a new skill.