Dangers and threats, moral dilemmas and temptations, increased pressure and ticking clocks, loss of control, power struggles

Witnessing a crime and being anonymously contacted with a warning to say nothing
Being intimidated into silence by thugs associated with the character's criminal ex
A whistleblower being sent incriminating sexual photos of himself as a warning to keep quiet
A teen who witnesses bullying being told that the same will happen to him if he talks 
A student seeing their teacher in a compromising situation being told that it's up to them if they pass or fail
The prosecution's star witness learning that someone sinister was in his elderly mother's home
A jury member receiving photos of her children under surveillance, along with a threatening note

Finding it hard to think straight
Feeling fearful and unsafe, even in their own home
Feeling watched and monitored
Having to hide the damning evidence (if it is being used as leverage)
Contacting friends and loved ones to make sure they are okay without raising alarms
Having to field questions about why the character is so quiet or seems distracted
Having to be on hand in case more incriminating mail or packages are delivered so they can be retrieved before family members discover the character's secrets 
Having to decide whether to share the threat with police or hide it
Having to decide whether to testify or "remember things differently" to muddy the case
Everyone telling the character what he or she should do
Procrastinating and making the situation worse
Loved ones pressuring the character to make a certain decision
Suffering from insomnia, ulcers, high blood pressure, and other health issues
Being unable to focus on work or school
Distractibility and irritability causing issues with the character's spouse and children