The worst reactions do seem to be after the 2nd jab, just from anecdotal evidence of talking to people I know.
After my 2nd Pfizer, I got a headache and cold sweats for a few hours that night. Eventually fell asleep and woke up feeling fine the next morning. Reported it as part of the data collection and no doubt was recorded as an “adverse reaction” which others will use in an attempt to scare people (there’s a few anti-vaxx fliers going around which love to quite these numbers).