I experience shaking, light headed, muscle twitching on celexa (citalopram). is this common?

Not common: Those are some more intense side effects you are describing although some of those side effects may be seen with antidepressants including citalopram. There are a category of side effects called extrapyramidal effects that you may be experiencing. You may want to talk to a doctor about what you are experiencing and determine if there are any other possibilities as to what is causing them.