With respect to your health, PLEASE FOLLOW YOUR DOCTOR'S ORDERS ABOUT YOUR BLOOD PRESSURE!
I am sure the other well-wishers here on bikeforums that are suggesting you try whatever, but they are not a qualified medical doctor who has seen you and your case!
Sure everyone means well, but often some people are willing to try something that was suggested on the internet, and THIS COULD BE HARMFUL!
Listen to your Doctor, if you have any questions or concerns, please consult with your Doctor, or at least with another Doctor or other highly qualified health care professional. Do not follow something just because you see it said by someone on the internet.
In my opinion, A GOOD RIDE, should not exhaust you! The length of said "Good Ride" need not be a specified distance. The Outside TEMPERATURE in F , along with the % of Relative Humidty and AIR QUALITY are very important factors. You cannot expect that riding in 95F with very muggy conditions (High Humidity) and somewhat stagnant air quality is going to be easy. Use common sense as a guide and try to be prepared for the conditions on hand on that particular day. It is not a badge of dishonor if some days, you cannot, or do not feel strong enough to go as much or as far.
Only you can determine what seems right. Rome wasn't built in a day. DO NOT THINK YOU MUST BUST YOUR RUMP BECAUSE SOMEBODY SAYS THAT IF YOU DON'T DO X miles while riding for a certain length of time.
I suggest that YOU ALWAYS WEAR A HELMET and THAT YOU ALWAYS CARRY A FULLY CHARGED PHONE, and You always carry at least a small water bottle.
For example, a good ride for me, consists of riding with pals in Saluda Shoals Park, which is a superb place to ride in my opinion with lengthy (5 miles of paved roads) with little or no automobile traffic, and the automobile traffic is typically about 20 mph through the park. The very tall Pine Trees and the wildlife that one routinely sees, rabbits, and turtles and sometimes snakes and the occasional deer sightings,........... The road is normal width two lane road, and there are speed bumps at certain places to make certain that automobile traffic is limited to slow speeds..................................Automobile access to the park is limited as you have a park ranger gatehouse at each park end that you must drive up to and register, or provide an annual subscription pass with bar code to the automated gate scanner/reader that raises the gate to enter the park. The Speedbumps do not have any effect on those who might be training for triathlons as one can to either side of them if you want to maintain a fast, bumpless pace. To give you an example, sometimes my pals and I have done as little as about six miles and other times we have gone more than 24 miles. We often ride what we refer to as CHIPS style (remember the mid-late seventies NBC Tv show...) side by side, having a conversation while riding. One riding pal who rode in our group there for two months last summer, who was a veteran marathon runner, but had never done a tri-athlon before then, trained with us in June, July, August 2018. She was fed all types of bull from the local idiots working in the bike stores. She was told by these young kids that they didn't downshift and just gut out the hills..........I mean how stupid is that, so she was having a hard time keeping up with the rest of us because she wasn't shifting to climb hills.... Once somebody asked her why was she fast except hills etc and she said the guys in the bike stores said they did it that way........so somebody in our group said, hey Linda, why do you think Fuji put so many gears on your bike and the Fuji engineers who selected the combination.........once somebody explained that it was something that you do so that you can maintain a pace/cadence that best suits you and allows for a swifter pace when you shift down or shift up when it becomes the time for you to do so. She said I was only doing what the bike shop guys said they did. We said you were listening to idiots, who probably barely graduated high school. She then approached it from an engineer's perspective and was shifting like crazy and the rest of us were unable to keep up with her. She was riding a vintage Fuji that she bought used on Craigs for $100 because it fit her very petite size. On a steel Fuji, she finished 4th in the Augusta HALF-IRONMAN in Sept 2018 in the 60-64 age group. It was her first competition while riding a bicycle. It was also her first swimming competition. She was a very experienced marathon runner but had not done any competitive swimming or bicycling. She trained for the swimming portion by swimming everyday in Lake Murray beginning in July 2018. You don't need to listen to dummies that tell you one thing or another........just because they might be twenty five year old half-wits working in a bike shop, or some really old one quarter wit like me, posting something on the internet.
Use your best judgement. What might be appropriate for some super-stud, young 18 to 25 year old half-wit that works in a bike shop and rides all the time, may not be realistic for someone who is no longer twenty-something.
Have Fun whenever and wherever you ride. If you don't like something about where and how you ride, then CHANGE what you don't like. Ride somewhere else, and/or if you're not comfortable riding in racing position (drop bars), there is absolutely nothing wrong with riding something in upright position with Northroad bars............ Ditto for something with either a mixte or step-through frame......... Not all bicycling is simply riding crouched forward wearing tight brightly colored spandex, pretending you're a tour de force as a Lance wannabee. There is nothing wrong with being a super-strong serious cyclist decked out in bright, tight fitting racing garb, as it is a well deserved badge of honor if you can spin it to win it and cruise at 30 mph but you don't need to try to kill yourself to get there. IF YOU REALLY WANT TO GET TO THAT POINT, IT IS POSSIBLE, BUT YOU WILL NEED TO BUILD UP OVER A SIGNIFICANT PERIOD OF TIME, UNLESS YOU'RE ALREADY A WORLD CLASS ATHLETE, WHICH LIKELY MAKES IT EASIER TO REACH THAT GOAL.
If you just make it a point to have a good fun ride, each time out and worry less about what the "serious" bikers do, you'll continue to ride. You will enjoy it more and more, and you'll likely see some benefit from regular and occasional riding. Don't wear yourself out. You're not doing the bike ride across Iowa tomorrow.
Get a comfortable bicycle seat and get a comfortable helmet and wear the helmet every time out.
Have fun. It does not matter how fast or slow , only that you GO and ride a little. You'll probably enjoy each ride and wish to ride again soon. Do not feel that you must go fast , because being aware and in control is more important. You do not want to crash. The pavement/asphalt/concrete is going to hurt you if you do crash.
Minimize your risk by always wearing a helmet. You can survive broken ribs, a broken clavicle, dislocated elbow, shoulder, fractured wrist, broken legs, broken arm, broken hip, knee injuries, road rash...etc but having your bare head bounce against the asphalt like a basketball and it could be fatal. Bike helmets do work.
MAKE YOUR OWN MEMORIES AND MAKE YOUR OWN RULES, RIDE AT YOUR OWN PACE...... It does not have to be a race!