while she was on the top step of a 2-step stool, her left leg went out from her, and she fell straight back, landing on the floor; her left knee keeps wanting to go out/ left leg kept wanting to buckle under her; she has 2 big bruises on arm, 1 bruise at her elbow and 1 bruise on her upper arm.; horrible pain in her left back/ pain was above her left kidney, and the pain ran from the bottom of her left rib cage to the bottom of her left butt cheek; pain ran from the bottom of her left rib cage; caller experienced pain from her kidney to her butt cheek; her arm was mildly sore; her left leg muscle is sore from above her left knee; This is a spontaneous report from a contactable consumer (patient). A 72-year-old female patient received the first dose of bnt162b2 (PFIZER-BIONTECH COVID-19 VACCINE, lot number: EL3249), via an unspecified route of administration on 22Jan2021 10:00AM at a single dose on the left arm for COVID-19 immunization. The patient did not receive any other vaccines within 4 weeks prior to receiving bnt162b2. Medical history included COVID-19 in Nov2020 and lost taste and smell. Reported she tested positive for the COVID-19 Virus in Nov2020. She said she was never sick during the time she had the COVID-19 Virus, though she lost her sense of taste and smell. She said she may have had a headache during that time, but she doesn't know if the headache was from the COVID-19 Virus or something else. She said anything she was experiencing during the time she had the COVID-19 Virus was kind of normal for her. Concomitant medications were none. Reported she got her first dose of the COVID-19 Vaccine on Friday, 22Jan2021, and thinks she may be having an adverse reaction. She said after she received her COVID-19 Vaccine, she was OK for the remainder of Friday, 22Jan2021, as well as, Saturday morning, 23Jan2021. Reported she was working outside the day before she had her first COVID-19 Vaccine dose (21Jan2021). She clarified she had a tree cut down in her yard, and she moved all the 3 foot length cut-up pieces of tree by herself. She had been moving tree cuttings. Her arm was mildly sore. Reported on Saturday (23Jan2021) in the middle of supper, she experienced a horrible pain in her left back. She clarified that the pain was above her left kidney, and the pain ran from the bottom of her left rib cage to the bottom of her left butt cheek. She said the pain was so bad she didn't think she was going to be able to finish eating supper. She said after supper she got on a heating pad and walked around the kitchen to see if that would help with the pain. She said she sat on the heating pad and walked around the kitchen 4 times that night. She said by Sunday (24Jan2021), the pain started to go away, and by Sunday night, she was OK. Reported this past Thursday, 28Jan2021, she was going to her mailbox. She said while she was walking out to her mailbox, she was holding onto her front porch post to go down the front porch stairs, and her left leg collapsed out from under her. She said she would have fallen if she wasn't holding on to the front porch post. She said she tried to continuing walking to the mailbox, and her left knee went out from under her again. She said her left leg kept wanting to buckle under her. She said after she got back inside her house, she sat down in a chair to read a book. She said she was making soup at the time and grabbed her husband's cane to walk to the kitchen. She said she is short and got on her 2-step stool to look in the freezer for vegetables. She said while she was on the top step of the stool, her left knee buckled and her left leg went out from under her. She said she fell straight back, landing on the floor. She said she has 2 big bruises on arm, 1 bruise at her elbow and 1 bruise on her upper arm. She said her left leg went out from under her again, yesterday (31Jan2021), while she was going to church. She said everything she has experienced since getting her COVID-19 Vaccine shot is only happening on her left side. Reported her left knee keeps wanting to go out and she has to be really careful when she walks. She said her left knee feels like it is wanting to buckle, like when someone runs up behind you and hits the backside of your knee. She said her left leg muscle is sore from above her left knee. She said she doesn't know if what she is experiencing is from getting her first COVID-19 Vaccine dose, and she wanted to know if anyone else has reported a similar experience since receiving the COVID-19 Vaccine. For fall treatment, she took a couple of Aleve 220mg tablets (UPC Number: 325866555090, Lot Number: NAA6W3T, Expiration Date: Jun2021) on 28Jan2021, after she fell off her stool.  Reported she took another 2 Aleve 200mg tablets last night (31Jan2021) at 11:00PM. Reported she is pretty darn healthy and only takes 3 pills. No other details provided. Reported she is trying to lock her left knee when she walks, saying she can feel her left knee giving away.  She said she while she was walking down a small ramp at church on Sunday (31Jan2021) her left knee wanted to buckle from under her. She said she had to hold onto a railing while she was walking down the ramp, so she wouldn't fall. She said she is not used to her left knee trying to go out from under her. The reported adverse events did not require a visit to the emergency room or physician office. Outcome of events "horrible pain in her left back/ pain was above her left kidney, and the pain ran from the bottom of her left rib cage to the bottom of her left butt cheek" (back pain, rib pain, and buttocks pain) was recovered on 24Jan2021. Outcome of "her left knee keeps wanting to go out/ left knee kept wanting to buckle under her" (joint instability), and "her left leg muscle is sore from above her left knee" (myalgia) was not recovered. Outcome of the remaining events was unknown.