What kind of wildflowers are they?

I'm not sure. It was a mixture of many different kind, some annual, some perennial.

What is your soil type? Sun exposure? Could be you got the wrong mix for the type of soil/site you have. If you have a mix that likes dry, fast draining soil and your site holds to much water your plants will not be as sturdy...they will lean or lay and the flowers will turn up looking for the sun.
My site is fast draining and we've had several hard driving rains and hail storms..those that did lay down perked right back up within 24 hours.

Vera

i can think of several reasons why your flowers bent over. its fairly very common for wildflowers to lean over or grow s shaped. particularly if they are not mixed in with grasses and particularly in their first or second year..... the grasses help "support" the flowers and force them to "get vertical" to grow... flowers on the edge of a planting tend to bend over to get more sunlight and less competition compared to the middle...a 3' wide planting will have all edge flowers and not much middle. and younger plants seem to have thinner less stout stems ... as they mature the stalks tend to get thicker and stouter making it easier to support a full wet flower head.

sometimes heavy rains will cause the flower heads to become heavy and fall over - and they may stand back up again when they dry off - but not always.

sometimes if they are planted along a fence row or other sunlight blocking thing they will grow away from it to get more sunlight.

some people stake them to get them to standup if they are concerned about the appearance or to prevent them from smothering something they might be laying on ....

i usually leave my plants up all winter as they can provide food and shelter for birds in the winter and they can provide a nice winter interest .... i would trim them back in the spring and the perrenials should grow back no problem.

Overly-fertile soil can also cause this.