PEM Diary is a React Native mobile app designed to help individuals with ME/CFS track and document PEM episodes. Built from personal experience, this app serves as a handy tool to understand your condition
Post-exertional malaise (PEM) is a condition where you feel extremely tired and unwell after doing physical or mental activities that you could normally handle before. PEM is a defining characteristic of ME/CFS (Myalgic Encephalomyelitis/Chronic Fatigue Syndrome) and is also associated with Long COVID. Many people who suffer from PEM episodes struggle to accurately track and document the condition often using paper journals or diaries. This documentation gap often leads to challenges in receiving proper medical attention and understanding personal triggers.
For Add Jam's cofounder Michael, this challenge is something personal. After experiencing Glandular Fever during University, he faced nearly two decades of suspected mild PEM crashes, often dismissed by healthcare providers. A golf session in February 2025 triggered another episode, leading to a revelation: I had no body of evidence to take to my doctor and worse there was no clear and efficient way to log and track these health events.
ME/CFS actually affects millions of people worldwide but it is a condition that is complex with a lack of objective diagnostic markers. Patient self-tracking can become an invaluable data point in these circumstances often through personal journals or diaries. Existing health tracking applications such as Apple Health rarely cater to the specific needs of the ME/CFS community.
The primary challenges identified were:
PEM Diary was born from this necessity - a mobile application designed to help individuals living with ME/CFS or Long COVID track and document their PEM episodes with ease. The app serves as a central repository for critical information about PEM crashes, helping users build a comprehensive case for medical professionals.
All data is stored on the users device and can only leave it (via data export) when they want it to.
The app provides comprehensive tools for PEM tracking including an intuitive crash logging interface, detailed symptom tracking, activity correlation, historical data analysis, and export functionality. All of this is delivered through a React Native iOS and Android experience that puts accessibility and ease of use at the forefront of the design.
The form for tracking a PEM Episode is low effort yet detailed enough to give useful data for future analysis of the condition. We iterated on the design to make the form as straightforward and simple to use with the core data collected being:
We implemented a minimalist interface designed to reduce cognitive load, featuring clear typography, high-contrast elements, and straightforward navigation.
All this with no invasive third party data tracking, no analytics, no cloud services storing your data. Your data belongs to you and you only.
Beyond tracking, PEM Diary serves aims to help users get through their PEM episodes. It can be mentally tough when dealing with the typical symptoms of PEM especially when in a severe episode that can last weeks or months. We try to help users through this with:
We felt the sleep aid feature was particularly important for users experiencing PEM episodes, as sleep disturbances are a common symptom. We designed this feature to be simple enough to use even during cognitive impairment, with a minimalist audio player interface featuring clear, accessible controls and a curated selection of calming sounds specifically chosen to aid relaxation and sleep.
With privacy as a core tenant of our approach we approached PEM Diary as a mobile app with all data stored securely on device. With this as our starting point we started with wireframes and mockups in Figma.
The application was quickly designed in Figma with a focus on feeling as 'native' as possible. By this we mean aiming to make the app feel like it is just part of the operating system - using animations, navigation paradigms and styling that closesly matches app that come with the phone.
This meant at this early state of design decisions including utilising React Navigation modals and implementing native stack large headers on iOS were made. We also at this stage iterated on our form and defined the core data structure for what we are storing in the PEM Diary.
PEM Diary was built using a modern React Native stack to ensure cross-platform compatibility while maintaining native performance:
The development process maintained a strong focus on rapid prototyping and iteration, while ensuring performance optimisation, offline-first functionality, and robust data privacy and security measures were implemented from the start.
PEM Diary empowers individuals with ME/CFS by providing:
While PEM Diary was initially developed as a personal tool, it has evolved into a potentially valuable resource for the broader ME/CFS community. The app helps users document PEM episodes systematically, identify triggers and patterns, present structured evidence to healthcare providers, and better understand their condition.
PEM Diary represents Add Jam's commitment to creating technology that makes a real difference in people's lives. As a passion project without direct monetisation, it demonstrates how personal experiences can drive the development of solutions that benefit wider communities.
The development of PEM Diary highlighted several important insights. Personal experience proved to be a powerful driver for innovation, while the project reinforced the importance of user privacy and data control in healthcare applications. We also demonstrated that native-feeling experiences can be achieved with cross-platform tools, and that sometimes the best projects come from solving our own problems.
For developers interested in building similar healthcare-focused applications, key technical considerations included implementing secure local storage for sensitive health data, optimising performance for frequent data entry, creating an intuitive UI for users experiencing health challenges, and ensuring accessibility features work across platforms.
PEM Diary demonstrates Add Jam's capability to turn personal challenges into meaningful solutions. While it may have started as a tool for personal use, it showcases our expertise in React Native development, healthcare application design, user-centric product development, and cross-platform mobile applications.
If you're looking to develop a healthcare application or need expertise in React Native development, contact Add Jam to discuss your project.
I've had these 'episodes' for a long time but realised I had no clear picture of what had actually been happening. I figured I needed to find a simple way to log PEM episodes and I didn't want that data to be accessible to anyone else but me so PEM Diary was born. I'm customer number one for this app and fingers crossed it can help many others.
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