Earliest sign of systemic absorption of local anaesthetic is –
Manifestations of local anesthetic toxicity (including lidocaine & bupivacaine)

Early symptoms (Prodrome) Circumoral numbness, dizziness, tongue paresthesia, restlessness, tinnitus, agitation.
CNS symptoms :- These are biphasic i.e. excitation (convulsions, restlessness, agitation & tinnitus), followed by depression (drowsiness, disorientation, respiratory depression, unconsciousness).
Cardiovascular manifestations :- hypotension, cardiac arrest, coma.
Convulsions
Circulatory collapse
Circumoral numbness
Respiratory arrest