Is trembling normal for an 18-month-old?
I think it's delightful that you have such an enthusiastic daughter! She's overflowing with excitement. Children vary in how they show strong emotion, and your child seems to be among the more demonstrative. Enjoy it. This behavior sounds normal to me, and it's not dangerous provided she's not falling over or hitting something. For this or any other behavior you think is unusual, videotape it and bring the tape in to your health care provider to review and to check on your child's development
generally. Most practitioners have access to a recorder and monitor. Children rarely do what you'd like in a health care provider's office, so a very short tape segment helps to clarify what the behavior is all about.