Some info on vaccinations:
Severe reactions to vaccinations usually happen within 12 hours.
Any vaccine may cause some animals to be 'sluggish' for a day or two afterwards, however may not affect some animals one bit.
More than 2 vaccinations given at the same time increase the likelihood of 'sluggishness'.
Vaccinating a sick animal is generally not advised. If your animal is sick don't wait until they are due for vaccinations to combine the trip, your pet probably won't be vaccinated then if it is sick.
Different name brands of vaccines may contribute to reactions or 'sluggishness'. (we changed brands of vaccines a year ago because of the number of 'sluggish' animal calls we were recieving not to mention the number of vaccine site bumps that persisted up to 4 weeks later. The brand of vaccine we are using now has almost completely stopped those worried owner calls we were getting.)
While no vaccine is a 100% guarantee, however not vaccinating increases your pets risk dramatically of getting a disease.
Just because you (or your parents, or uncle, or great, great aunt so-and-so) had a pet that never recieved vaccinations/heartworm preventative doesn't mean that those things aren't necessary, it just means you (or your parents, or uncle, or great, great aunt so-and-so) were just lucky to the benefit of your pet.
Sarcoma's (type of cancer) can come from ANY injection not just vaccines.