Oracle Database Discussions

I have a sequence X_seq that had a maxvalue of 65535(set at the time it was created).

But now, when I do

select X_seq.nextval from dual
*
ERROR at line 1:
ORA-08004: sequence X_SEQ.NEXTVAL exceeds MAXVALUE and cannot be instantiated

select X_seq.currval from dual
*
ERROR at line 1:
ORA-08002: sequence X_SEQ.CURRVAL is not yet defined in this session

Interestingly,
SELECT last_number,max_value from user_sequences where sequence_name = 'X_SEQ';

LAST_NUMBER MAX_VALUE
----------- ----------
65536 65535
What I don't understand is that why could the last_number be greated than the max_value and what is this last_number

Thanks