"Jimjams" is not particularly common today, but when it is used in current American English it means simply "jitters." Etymologists aren't sure about the origin of the term.

What are Jim jams?

extreme nervousness; jitters.

What is the meaning of pj's?

(pidʒeɪz ) also pj's. plural noun. Pjs are the same as pajamas. [US, informal] I work from home and live in my pjs most of the time.