Paragraph headings followed by line space and no indent, but indents or line space for “unheaded” paragraphs [closed]

Question

I would like to have paragraphs with a heading followed by a line space (i.e. blank line) and then no indent for paragraph text after that line space. By "paragraphs with a heading", I mean paragraphs created with an explicit command - e.g. \paragraph{This is the Paragraph Heading} - and with paragraph (and subparagraph) numbering turned on - e.g. by \setcounter{secnumdepth}{5}. I would like similar formatting for subparagraphs with a heading.

I have found solutions here for this that work (see below).

However, for paragraphs without a heading (i.e. paragraphs created by two line returns in source text - the first ending a line, the second giving a line space), I would like either to retain the default indentation or to have a line space (blank line) before the paragraph text. I'd also like to be able to try both and to switch easily, to see what the document looks like with each.

The general notion here is that a paragraph created and signaled with a heading would not need another signal by indentation, but a paragraph created otherwise, without a heading, would need a signal, by indentation or by a blank line.
This seems reasonable to me as a style (comments by typographical experts appreciated).

The solutions for paragraph headings seem to turn off the default indentation and any preceding line space for paragraphs without a heading, and also to have other effects on spacing in text.
Quite obviously, I do not understand at all well the meaning of the syntax of these solutions, but I am trying to finish a paper without having to do too much more LaTeX study.

Also, I wish to set this style or behavior generally, without extra commands at each instance. And I am not using KOMA (and fear getting into it at all right now - though perhaps later).

The solutions I've tried include the following (which can perhaps accomplish what I'd like with minor alterations):

• Renew Paragraph Command Solutions (3 of them):

  \makeatletter
  \renewcommand\paragraph{%
     \@startsection{paragraph}{4}{0mm}%
        {-\baselineskip}%
        {.5\baselineskip}%
        {\normalfont\normalsize\bfseries}}
  \makeatother
  
  \makeatletter
  \renewcommand\paragraph{\@startsection{paragraph}{4}{\z@}%
        {-3.25ex\@plus -1ex \@minus -.2ex}%
        {1.5ex \@plus .2ex}%
        {\normalfont\normalsize\bfseries}}
  \makeatother
  
  \makeatletter
  \renewcommand\paragraph{\@startsection{paragraph}{4}{\z@}%
    {-3.25ex \@plus -1ex \@minus -0.2ex}%
    {0.01pt}%
    {\raggedsection\normalfont\sectfont\nobreak\size@paragraph}%
  }
  \makeatother
  

• Solution using titlesec:

  \usepackage{titlesec}
  
  \titleformat{\paragraph}
      {\normalfont\bfseries}
      {}
      {0pt}
      {}
  

• My "minimal example":

  \paragraph{This is the Paragraph Heading}
  
  This is the first line of the paragraph, and I would like it not indented, 
  and with a line space (blank line) before (bewteen its first line and its 
  heading).  I have found solutions that work for this.
  
  This is another paragraph or sub-paragraph, created without a heading, and
  I would like it signaled somehow, either by an indentation or a line space 
  (blank line) before.  The solutions for the paragraph heading don't work
  for this (at least not as they are now).
  

I would like this behavior to continue until the next paragraph heading.