Determine Whether the Following Is Valid or Invalid

Short Answer

Determine whether the following is valid or invalid:
I finally discovered the mystery of why hard beds are good for you. Here's the story: If you have a hard bed, then you cannot stay comfortable for long periods, and when you can't stay comfortable for long periods, you roll around a lot. If you roll around a lot, then your joints don't ache from being in one position for too long. Therefore, if your joints ache in the morning from sleeping too long in one position,
then you don't have a hard bed.