You're afraid of being reborn over and over again forever, facing suffering again and again, and of relearning all of this over and over again.
Yet some others are afraid of death, because they don't believe in rebirth and think that they will cease to exist at death. They don't want to stop existing. They are afraid of ceasing to exist.
Both of these appear to be opposite, but they are really two sides of the same coin. They are symptoms of the same disease (dis-ease). The fear arises from clinging to something that is impermanent and unstable.
(i. The aggregates)
"For one who loves form, who is fond of form, who cherishes form, who
does not know or see, as it actually is present, the cessation of
form, there occurs the thought, 'The Tathagata exists after death' or
'The Tathagata does not exist after death' or 'The Tathagata both
exists and does not exist after death' or 'The Tathagata neither
exists nor does not exist after death.'
"For one who loves feeling...
"For one who loves perception...
"For one who loves fabrications...
"For one who loves consciousness, who is fond of consciousness, who
cherishes consciousness, who does not know or see, as it actually is
present, the cessation of consciousness, there occurs the thought,
'The Tathagata exists after death' or 'The Tathagata does not exist
after death' or 'The Tathagata both exists and does not exist after
death' or 'The Tathagata neither exists nor does not exist after
death.'
"But for one who doesn't love form, who isn't fond of form, who
doesn't cherish form, who knows & sees, as it actually is present, the
cessation of form, the thought, 'The Tathagata exists after death' or
'The Tathagata does not exist after death' or 'The Tathagata both
exists and does not exist after death' or 'The Tathagata neither
exists nor does not exist after death' doesn't occur.
"For one who doesn't love feeling...
"For one who doesn't love perception...
"For one who doesn't love fabrication...
"For one who doesn't love consciousness, who isn't fond of
consciousness, who doesn't cherish consciousness, who knows & sees, as
it actually is present, the cessation of consciousness, the thought,
'The Tathagata exists after death' or 'The Tathagata does not exist
after death' or 'The Tathagata both exists and does not exist after
death' or 'The Tathagata neither exists nor does not exist after
death' doesn't occur.
"This is the cause, this is the reason, why that has not been declared
by the Blessed One."
(ii. Becoming)
"But, my friend, would there another line of reasoning, in line with
which that has not been declared by the Blessed One?"
"There would, my friend. "For one who loves becoming, who is fond of
becoming, who cherishes becoming, who does not know or see, as it
actually is present, the cessation of becoming, there occurs the
thought, 'The Tathagata exists after death' or 'The Tathagata does not
exist after death' or 'The Tathagata both exists and does not exist
after death' or 'The Tathagata neither exists nor does not exist after
death.'
"But for one who doesn't love becoming, who isn't fond of becoming,
who doesn't cherish becoming, who knows & sees, as it actually is
present, the cessation of becoming, the thought, 'The Tathagata exists
after death' or 'The Tathagata does not exist after death' or 'The
Tathagata both exists and does not exist after death' or 'The
Tathagata neither exists nor does not exist after death' doesn't
occur.
"This, too, is a line of reasoning in line with which that has not
been declared by the Blessed One."