Should I pursue a PhD in STEM?

Whether or not to pursue a PhD will depend on a number of factors. These days, many professions require more and more certification and proof of education. However, a PhD is usually only require in the STEM field for positions that are either focussed on research, such as a research scientist position, or on a specialized field, such as many 'wet labs' in biological research, or more specialized knowledge jobs. Other than these roles, a Master's or other accreditation like professional certificates/MBAs etc. can be used for career advancement. For those interested in an academic career, a PhD is still the fundamental requirement. 

If you do choose to do a PhD, where you do a PhD will influence the amount and type of work that you do. For example, in the EU, the UK, Australia, and some other places, a PhD is usually three years of research with no or minimal extra course work. In the US, though, a PhD typically takes over 4 years and requires the student to take several classes at a graduate level. 
While in your program, you will need to spend a lot of time focusing on publication pressures. PhD students, these days, are required to produced 1-3 papers during their PhD in high impact journals. In many institutions, this is a high stress environment and can lead to increased mental health stress. If you are passionate and build a strong social structure, this can be an enjoyable experience, albeit a trying one.