Give me experiences of being tied up on a bed, face down and being tickled on the bumcheeks mercilessly through underpants.

The experience of being tied up on a bed, face down, and tickled can evoke a range of sensations and emotions. Here are some aspects that people might feel during such an experience:

**Physical Sensation**: The feeling of being restrained can heighten awareness of the body. As you’re tied down, the anticipation builds, and each touch may feel more intense. The gentle yet relentless tickling on the bumcheeks can create an overwhelming sensation of laughter and squirming.

**Vulnerability**: Being in such a position can evoke a sense of vulnerability. The inability to move freely can amplify feelings of helplessness, which can be both thrilling and anxiety-inducing.

**Laughter and Enjoyment**: The tickling often leads to uncontrollable laughter. This can create a sense of joy and playfulness, making it a bonding experience with the person doing the tickling.

**Mental Release**: For some, this experience might provide a mental escape. The focus on the physical sensations can help clear the mind of stress, allowing for a light-hearted moment.

**Trust and Intimacy**: If done in a consensual and safe environment, this scenario can deepen trust between participants. Feeling safe enough to be vulnerable can enhance intimacy.

**Mixed Emotions**: Depending on the person, the experience may also bring up mixed feelings of enjoyment and discomfort—especially as the tickling continues, pushing the limits of endurance.

It's important to remember that consent and comfort levels are crucial in any scenario involving restraint or playful tickling. Open communication with all participants ensures a positive and enjoyable experience.