The truth is, everybody is different; if you're high-strung, your daily stress level will be greater than that of someone who is laid-back. A good way to judge if you're too tense is if your relationships, job and mental or physical health have deteriorated. Has your sleep or appetite changed? Do you still enjoy things that have given you pleasure in the past?
If any of those factors have shifted, you may be in stress overdrive, which means you need to pinpoint the source of your tension and, ideally, eliminate it. If your biggest thorn is something you can't get rid of, such as nagging in-laws, try to minimize your exposure.
Perhaps more vital is recognizing how you react to stress. Do you shut down or spread negativity? Once you have a handle on that, you can work on developing a healthier response, like releasing those bottled-up feelings at the gym or chatting with a supportive friend. Learning to prepare for stress can help, too. If talking to your landlord gets you riled up, put yourself in your comfort zone by listening to soothing music before you pick up the phone so you're less affected by the conversation. Remember, once you recognize the problem, you have the power to fix it.