Forms :: Database 10g - Calling Sequence

CREATE SEQUENCE hyd1_seq
START WITH 2100000
INCREMENT BY 1
NOCACHE
NOCYCLE;

this is how i created a sequence in database 10g.

if :SHIP_MSTR.PLACE_FROM = 'hyd1' then
SELECT hyd1_seq.NEXTVAL
INTO :SHIP_MSTR.BILL_ID
FROM dual;

this is how iam calling sequence in form.my problem is once the sequence is generated in form and even if i am not saving a form its generating next value next time.what i want to do is if i am not saving the form that sequence number should again come in bill_id.