If you have the heebie-jeebies, you're worried, anxious, or jumpy. Haunted houses, for example, give many people the heebie-jeebies, while others get the heebie-jeebies from circus clowns.
If something gives you the heebie-jeebies, it makes you very nervous. The word is especially useful when something — or someone — gives you the creeps, but you can't put your finger on exactly what it is that makes you so jittery. Heebie-jeebies first appeared in print in the U.S., originally in a 1923 "Barney Google" cartoon by Billy DeBeck, who is also credited with inventing the word horsefeathers, which means "nonsense."