Are you talking about Postural Orthostatic Tachycardia Syndrome?
If that is what you are referring to, I do not understand why you need to apologize to anyone for anything. You have a physical illness. How is having POTS any different than cancer, MS, diabetes, or any other physical illness over which you had no control.
Personally, I would just reach out to them and tell them how much you have missed them and how much you look forward to reconnecting with them.
Getting sick is not your fault. It is no one's fault. Your friends will understand if they are true friends. Those who refuse to understand were not true friends to begin with.
Reconnecting with anyone after a long period of time can be rough, if not impossible. Make a good, solid effort to reconnect with those that you truly did miss and if they feel they cannot make time for you anymore then look for a new outlet of friends.
gather them , plan to go some where fun and right before reaching the place , go like guys im sorry blah blah blah and theyl be like aww its k and then a 1 min awkward silence and then bam u reach u the fun place , have fun and it'd be as if u neveh left
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