What is the difference between population bottleneck and consanguinity?

what is, and why is there a difference in disease incidences and allele frequency in a bottleneck population and in consanguinity? please help. i have to relate it back to the amish people. i don't understand why there i rapid increase in disease in a consanguinity but a slower one in the bottleneck, is it because there is a reduction in gene pool in consanguinity and thus deleterious mutations are more likely to spread..... and i don't understand why does the allele frequency in consanguinity examples all decrease? im not sure, please help. thank you.